Merge of 10.0-mdev26 feature tree into 10.0-base.

Global transaction ID is prepended to each event group in the binlog.

Slave connect can request to start from GTID position instead of specifying
file name/offset of master binlog. This facilitates easy switch to a new
master.

Slave GTID state is stored in a table mysql.rpl_slave_state, which can be
InnoDB to get crash-safe slave state.

GTID includes a replication domain ID, allowing to keep track of distinct
positions for each of multiple masters.

Fixed MDEV-4033 Unable to use slave's temporary directory /tmp - Can't create/write to file '/tmp/SQL_LOAD-' (Errcode: 17 "File exists")
- Cache value of check_temp_dir() to avoid race condition
- Set $rpl_server_count to avoid error in show_rpl_debug_info.inc

mysql-test/suite/multi_source/info_logs.test:
  Set $rpl_server_count
mysql-test/suite/multi_source/multisource.test:
  Set $rpl_server_count
mysql-test/suite/multi_source/relaylog_events.test:
  Set $rpl_server_count
mysql-test/suite/multi_source/reset_slave.test:
  Set $rpl_server_count
mysql-test/suite/multi_source/simple.test:
  Set $rpl_server_count
mysql-test/suite/multi_source/skip_counter.test:
  Set $rpl_server_count
mysql-test/suite/multi_source/status_vars.test:
  Set $rpl_server_count
sql/slave.cc:
  Cache value of check_temp_dir() to avoid race condition

         Syntax modified to allow statements:
               ALTER TABLE ADD/DROP COLUMN
               ALTER TABLE ADD/DROP INDEX
               ALTER TABLE ADD/DROP FOREIGN KEY
               ALTER TABLE ADD/DROP PARTITION
               ALTER TABLE CHANGE COLUMN
               ALTER TABLE MODIFY COLUMN
               DROP INDEX
         to have IF (NOT) EXISTS options.
         Appropriate implementations added to mysql_alter_table().
      
      per-file comments:
        mysql-test/r/alter_table.result
      MDEV-318 IF (NOT) EXIST clauses for ALTER TABLE (MWL #252).
              test result updated.
        mysql-test/r/fulltext.result
      MDEV-318 IF (NOT) EXIST clauses for ALTER TABLE (MWL #252).
        mysql-test/r/partition.result
              test result updated.
      MDEV-318 IF (NOT) EXIST clauses for ALTER TABLE (MWL #252).
        mysql-test/t/alter_table.test
              tests added.
      MDEV-318 IF (NOT) EXIST clauses for ALTER TABLE (MWL #252).
        mysql-test/t/fulltext.test
      MDEV-318 IF (NOT) EXIST clauses for ALTER TABLE (MWL #252).
              tests added.
        mysql-test/t/partition.test
      MDEV-318 IF (NOT) EXIST clauses for ALTER TABLE (MWL #252).
              tests added.
        sql/field.cc
      MDEV-318 IF (NOT) EXIST clauses for ALTER TABLE (MWL #252).
              create_if_not_exists field added.
        sql/field.h
      MDEV-318 IF (NOT) EXIST clauses for ALTER TABLE (MWL #252).
              create_if_not_exists field added.
        sql/partition_info.h
      MDEV-318 IF (NOT) EXIST clauses for ALTER TABLE (MWL #252).
              has_unique_name made public.
        sql/sp_head.cc
      MDEV-318 IF (NOT) EXIST clauses for ALTER TABLE (MWL #252).
        sql/sql_class.cc
      MDEV-318 IF (NOT) EXIST clauses for ALTER TABLE (MWL #252).
              create_if_not_exists inited.
        sql/sql_class.h
      MDEV-318 IF (NOT) EXIST clauses for ALTER TABLE (MWL #252).
              create_if_not_exists inited.
        sql/sql_lex.cc
      MDEV-318 IF (NOT) EXIST clauses for ALTER TABLE (MWL #252).
              check_exists inited.
        sql/sql_lex.h
      MDEV-318 IF (NOT) EXIST clauses for ALTER TABLE (MWL #252).
              check_exists inited.
        sql/sql_parse.cc
      MDEV-318 IF (NOT) EXIST clauses for ALTER TABLE (MWL #252).
        check_exists inited.
        sql/sql_table.cc
      MDEV-318 IF (NOT) EXIST clauses for ALTER TABLE (MWL #252).
              handle_if_exists_options() added.
              it's called in mysql_alter_table().
        sql/sql_trigger.cc
      MDEV-318 IF (NOT) EXIST clauses for ALTER TABLE (MWL #252).
              check_exists instead of drop_if_exists.
        sql/sql_view.cc
      MDEV-318 IF (NOT) EXIST clauses for ALTER TABLE (MWL #252).
              check_exists instead of drop_if_exists.
        sql/sql_yacc.yy
      MDEV-318 IF (NOT) EXIST clauses for ALTER TABLE (MWL #252).
              sintax modified.

    The patch contributed by Konstantin Osipov applied.
    Native comments:
      Implement multiple user-level locks per connection.

      GET_LOCK() function in MySQL allows a connection  to hold at most
      one user level lock. Taking a new lock automatically releases the
      old lock, if any.

      The limit of one lock per session existed since  early versions
      of MySQL didn't have a deadlock detector for SQL locks.
      MDL patches in MySQL 5.5 added a deadlock detector,
      so starting from 5.5 it became possible to take multiple locks
      in any order -- a deadlock, should it occur, would be detected
      and an error returned to the client which closed the wait chain.

      This is exactly what is done in this patch: ULLs are moved
      to use MDL subsystem.

This fixes that by default LOAD DATA INFILE will not generate the error:
"Multi-statement transaction required more than 'max_binlog_cache_size' bytes of storage..."


mysql-test/suite/sys_vars/r/max_binlog_cache_size_basic.result:
  Updated test case
mysql-test/suite/sys_vars/r/max_binlog_stmt_cache_size_basic.result:
  Updated test case
sql/sys_vars.cc:
  Increase default value of max_binlog_cache_size and max_binlog_stmt_cache_size to ulonglong_max.

The selectivity of a range degenerated into a point never should be set to 0.

(because only there it  makes any sense)

mysql-test/r/mysqld--help.result:
  that's default to number of CPUs
mysql-test/suite/archive/discover.test:
  move_file uses rename(2), which may end up
  with "Invalid cross-device link"
mysql-test/suite/archive/partition_archive.test:
  on Solaris the error message is different

fix semisync plugins and tests to work with both with static and dynamic linking

MySQL 5.1 and 5.2 alpha trees.

avoid unnecessary strlen()'s

(but support the scopeless mysql style too).
always output status/system variables in the correct lettercase

and INFORMATION_SCHEMA.ALL_PLUGINS table
with condition pushdown for I_S.ALL_PLUGINS
and a  new status variable to cound successful dlopen's

Change Item_func_get_system_var::val_xxx functions to use that.

mysql-test/t/variables.test:
  @@GLOBAL.INIT_CONNECT is never NULL anymore. Nor it ever was.
  It was a bug that empty string system variables appeared as NULL
  in the *integer context* (but not in a string, real, or decimal context!)

instead of "used storage engine" and similar changes.

implement ./mtr --dry-run