simplify open_table_def()

* print "table doesn't exist in engine" when a table doesn't exist in the engine,
  instead of "file not found" (if no file was involved)
* print a complete filename that cannot be found ('t1.MYI', not 't1')
* it's not an error for a DROP if a table doesn't exist in the engine (or some table
  files cannot be found) - if the DROP succeeded regardless

           locks on the table

Fixing the partitioning specifics after TRUNCATE TABLE in
bug-42643 was fixed.

Reorganize of code to decrease the size of the giant switch
in mysql_execute_command, and to prepare for future parser
reengineering. Moved code into Sql_statement objects.

Updated patch according to davi's review comments.

libmysqld/CMakeLists.txt:
  Added new files.
libmysqld/Makefile.am:
  Added new files.
mysql-test/r/not_partition.result:
  now returning error on partitioning commands
  if partitioning is not enabled.
mysql-test/r/partition_disabled.result:
  There is no partition handlerton, so it cannot
  find the specified engine in the .frm file.
mysql-test/r/partition_truncate.result:
  Updated test results.
mysql-test/suite/parts/inc/partition_mgm.inc:
  Added check that TRUNCATE PARTITION does not delete on failure.
mysql-test/suite/parts/r/partition_debug_sync_innodb.result:
  updated results.
mysql-test/suite/parts/r/partition_mgm_lc0_archive.result:
  updated results.
mysql-test/suite/parts/r/partition_mgm_lc1_archive.result:
  updated results.
mysql-test/suite/parts/r/partition_mgm_lc2_archive.result:
  updated results.
mysql-test/suite/parts/t/partition_debug_sync_innodb.test:
  Test case for this bug.
mysql-test/t/not_partition.test:
  Added check for TRUNCATE PARTITION without partitioning.
mysql-test/t/partition_truncate.test:
  Added test of TRUNCATE PARTITION on non partitioned table.
sql/CMakeLists.txt:
  Added new files.
sql/Makefile.am:
  Added new files.
sql/datadict.cc:
  Moved out the storage engine check into an own
  function, including assert for lock.
sql/datadict.h:
  added dd_frm_storage_engine.
sql/sql_alter_table.cc:
  moved the code for SQLCOM_ALTER_TABLE in mysql_execute_command
  into its own file, and using the Sql_statement object to
  prepare for future parser reengineering.
sql/sql_alter_table.h:
  Created Sql_statement object for ALTER TABLE.
sql/sql_lex.cc:
  resetting m_stmt.
sql/sql_lex.h:
  Temporary hack for forward declaration of enum_alter_table_change_level.
sql/sql_parse.cc:
  Moved out ALTER/ANALYZE/CHECK/OPTIMIZE/REPAIR TABLE
  from the giant switch into their own Sql_statement
  objects.
sql/sql_parse.h:
  Exporting check_merge_table_access.
sql/sql_partition_admin.cc:
  created Sql_statement for
  ALTER TABLE t ANALYZE/CHECK/OPTIMIZE/REPAIR/TRUNCATE
  PARTITION. To be able to reuse the TABLE equivalents.
sql/sql_partition_admin.h:
  Added Sql_statement of partition admin statements.
sql/sql_table.cc:
  Moved table maintenance code into sql_table_maintenance.cc
sql/sql_table.h:
  Moved table maintenance code into sql_table_maintenance.h
  exporting functions used by sql_table_maintenance.
sql/sql_table_maintenance.cc:
  Moved table maintenance code from sql_table.cc
sql/sql_table_maintenance.h:
  Sql_statement objects for ANALYZE/CHECK/OPTIMIZE/REPAIR TABLE.
  Also declaring the keycache functions.
sql/sql_truncate.cc:
  Moved code from SQLCOM_TRUNCATE in mysql_execute_command into
  Truncate_statement::execute.
  Added check for partitioned table on TRUNCATE PARTITION.
  Moved locking fix for partitioned table into
  Alter_table_truncate_partition::execute.
sql/sql_truncate.h:
  Truncate_statement declaration (sub class of Sql_statement).
sql/sql_yacc.yy:
  Using the new Sql_statment objects.

Remove acquisition of LOCK_open around file system operations,
since such operations are now protected by metadata locks.
Rework table discovery algorithm to not require LOCK_open.

No new tests added since all MDL locking operations are covered
in lock.test and mdl_sync.test, and as long as these tests
pass despite the increased concurrency, consistency must be
unaffected.

mysql-test/t/disabled.def:
  Disable NDB tests due to Bug#55799.
sql/datadict.cc:
  No longer necessary to protect ha_create_table() with
  LOCK_open. Serial execution is now ensured by metadata
  locks.
sql/ha_ndbcluster.cc:
  Do not manipulate with LOCK_open in cluster code.
sql/ha_ndbcluster_binlog.cc:
  Do not manipulate with LOCK_open in cluster code.
sql/ha_ndbcluster_binlog.h:
  Update function signature.
sql/handler.cc:
  Implement ha_check_if_table_exists().
  @todo: some engines provide ha_table_exists_in_engine()
  handlerton call, for those we perhaps shouldn't
  call ha_discover(), to be more efficient.
  Since currently it's only NDB, postpone till
  integration with NDB.
sql/handler.h:
  Declare ha_check_if_table_exists() function.
sql/mdl.cc:
  Remove an obsolete comment.
sql/sql_base.cc:
  Update to a new signature of close_cached_tables():
  from now on we always call it without LOCK_open.
  Update comments.
  Remove get_table_share_with_create(), we should
  not attempt to create a table under LOCK_open.
  Introduce get_table_share_with_discover() instead,
  which would request a back off action if the table
  exists in engine.
  Remove acquisition of LOCK_open for 
  data dictionary operations, such as check_if_table_exists().
  Do not use get_table_share_with_create/discover for views,
  where it's not needed.
  Make tdc_remove_table() optionally acquire LOCK_open
  to simplify usage of this function.
  Use the right mutex in the partitioning code when
  manipulating with thd->open_tables.
sql/sql_base.h:
  Update signatures of changes functions.
sql/sql_insert.cc:
  Do not wrap quick_rm_table() with LOCK_open acquisition, 
  this is unnecessary.
sql/sql_parse.cc:
  Update to the new calling convention of tdc_remove_table().
  Update to the new signature of close_cached_tables().
  Update comments.
sql/sql_rename.cc:
  Update to the new calling convention of tdc_remove_table().
  Remove acquisition of LOCK_open around filesystem
  operations.
sql/sql_show.cc:
  Remove get_trigger_table_impl().
  Do not acquire LOCK_open for a dirty read of the trigger
  file.
sql/sql_table.cc:
  Do not acquire LOCK_open for filesystem operations.
sql/sql_trigger.cc:
  Do not require LOCK_open for trigger file I/O.
sql/sql_truncate.cc:
  Update to the new signature of tdc_remove_table().
sql/sql_view.cc:
  Do not require LOCK_open for view I/O.
  Use tdc_remove_table() to expel view share.
  Update comments.
sql/sys_vars.cc:
  Update to the new signature of close_cached_tables().

The problem was that TRUNCATE TABLE didn't take a exclusive
lock on a table if it resorted to truncating via delete of
all rows in the table. Specifically for InnoDB tables, this
could break proper isolation as InnoDB ends up aborting some
granted locks when truncating a table.

The solution is to take a exclusive metadata lock before
TRUNCATE TABLE can proceed. This guarantees that no other
transaction is using the table.

Incompatible change: Truncate via delete no longer fails
if sql_safe_updates is activated (this was a undocumented
side effect).

libmysqld/CMakeLists.txt:
  Add new files to the build list.
libmysqld/Makefile.am:
  Add new files to the build list.
mysql-test/extra/binlog_tests/binlog_truncate.test:
  Add test case for Bug#42643
mysql-test/include/mix1.inc:
  Update test case as TRUNCATE TABLE now grabs a exclusive lock.
  Ensure that TRUNCATE waits for granted locks on the table.
mysql-test/suite/binlog/t/binlog_truncate_innodb.test:
  As with other data modifying statements, TRUNCATE is still not
  possible in a transaction with isolation level READ COMMITTED
  or READ UNCOMMITED. It would be possible to implement so, but
  it is not worth the effort.
mysql-test/suite/binlog/t/binlog_truncate_myisam.test:
  Test under different binlog formats.
mysql-test/suite/binlog/t/disabled.def:
  Re-enable test case.
mysql-test/t/innodb_bug38231.test:
  Truncate no longer works with row-level locks.
mysql-test/t/mdl_sync.test:
  Ensure that a acquired lock is not given up due to a conflict.
mysql-test/t/partition_innodb_semi_consistent.test:
  End transaction as to release metadata locks.
mysql-test/t/truncate.test:
  A metadata lock is now taken before the object is verified.
sql/CMakeLists.txt:
  Add new files to the build list.
sql/Makefile.am:
  Add new files to the build list.
sql/datadict.cc:
  Introduce a new file specific for data dictionary operations.
sql/datadict.h:
  Add header file.
sql/sql_base.cc:
  Rename data dictionary function.
sql/sql_bitmap.h:
  Include dependency.
sql/sql_delete.cc:
  Move away from relying on mysql_delete() to delete all rows of
  a table. Thus, move any bits related to truncate to sql_truncate.cc
sql/sql_delete.h:
  Remove parameter.
sql/sql_parse.cc:
  Add protection against the global read lock -- a intention
  exclusive lock can be acquired in the truncate path.
sql/sql_show.cc:
  Add sync point for testing scenarios where a pending flush
  is ignored.
sql/sql_truncate.cc:
  Acquire a shared metadata lock before accessing table metadata.
  Upgrade the lock to a exclusive one if the table can be re-created.
  Rework binlog rules to better reflect the requirements.
sql/sql_yacc.yy:
  Set appropriate lock types for table to be truncated.
sql/table.h:
  Move to data dictionary header.