If an outer query is broken, a subquery might not even get set up.
EXPLAIN EXTENDED did not expect this and merrily tried to de-ref all
of the half-setup info.

We now catch this case and print as much as we have, as it doesn't cost us
anything (doesn't make regular execution slower).

backport from 5.1

mysql-test/r/explain.result:
  Show that EXPLAIN EXTENDED with subquery and illegal out query doesn't crash.
  Show also that SHOW WARNINGS will render an additional Note in the hope of
  being, well, helpful.
mysql-test/t/explain.test:
  If we have only half a query for EXPLAIN EXTENDED to print (i.e.,
  incomplete subquery info as outer query is illegal), we should
  provide the user with as much info as we easily can if they ask
  for it. What we should not do is crash when they come asking for
  help, that violates etiquette in some countries.
sql/item_subselect.cc:
  If the sub-query's actually set up, print it. Otherwise, elide.

      
This patch fixes some typos and poorly formulated sentences in
the output from mysqld --help --verbose.

Some of the problems described in the bug report are already
handled by the patch for Bug#49447, and are therefore not
included in this patch.

START SLAVE UNTIL MASTER ... specifies only SQL thread to stop.
rpl_slave_skip erronously deployed waiting for stop of both threads.

Corrected with deploying the correct macro.
Notice, earlier a similar bug@47749 was fixed in mysql-trunk.

mysql-test/suite/rpl/t/rpl_slave_skip.test:
  changing two waiting calls for offline of both threads into waiting for SQL to stop.

for same data when using bit fields

Problem: checksum for BIT fields may be computed incorrectly 
in some cases due to its storage peculiarity.

Fix: convert a BIT field to a string then calculate its checksum.


mysql-test/r/myisam.result:
  Fix for bug#51304: checksum table gives different results 
  for same data when using bit fields
    - test result.
mysql-test/t/myisam.test:
  Fix for bug#51304: checksum table gives different results 
  for same data when using bit fields
    - test case.
sql/sql_table.cc:
  Fix for bug#51304: checksum table gives different results 
  for same data when using bit fields
    - convert BIT fields to strings calculating its checksums
  as some bits may be saved among NULL bits in the record buffer.

disabling the test to not run on PB

mysql-test/t/mysql_upgrade.test:
  For execution, mostly testing the presence of the binary anyway.

POSIX standard, reinitialization of a pthread_once is a gray
area, but it is needed to support subsequent initializations
of the client library.

mysys/charset.c:
  Reinitialize a pthread_once_t variable.

A client doing multiple mysql_library_init() and
mysql_library_end() calls over the lifetime of the process may
experience lost character set data, potentially even a
SIGSEGV.

This patch reinstates the reloading of character set data when
a mysql_library_init() is done after a mysql_library_end().

Item_field::print method does not take into
account fields whose values may be null.
The fix is to print 'NULL' if field value is null.


mysql-test/r/explain.result:
  test case
mysql-test/r/func_str.result:
  result fix
mysql-test/r/having.result:
  result fix
mysql-test/r/select.result:
  result fix
mysql-test/r/subselect.result:
  result fix
mysql-test/r/union.result:
  result fix
mysql-test/t/explain.test:
  test case
sql/item.cc:
  print 'NULL' if field value is null.

Fixed a syntax error in mysqld_multi.sh

The problem was that the CSV storage engine does not support NULL
fields, yet in some early 5.1 version the log tables (general_log
and slow_log) were created with null fields. On top of this, when
altering a CSV table column, all fields of the table must be NOT
NULL otherwise the alteration fails.

The solution is to ensure that during upgrade all columns of the
log tables are NOT NULL.

mysql-test/r/log_tables_upgrade.result:
  Add test case result for Bug#49823.
mysql-test/std_data/bug49823.CSV:
  Sample data for test.
mysql-test/std_data/bug49823.frm:
  Add a CSV table which mimics the general_log table, except that
  it contains a nullable column.
mysql-test/t/log_tables_upgrade.test:
  Add test case for Bug#49823.
scripts/mysql_system_tables_fix.sql:
  Ensure that all columns of the log tables are NOT NULL.

The test failed due to Bug #29790.
However, logics of the failing part does not need I_S selecting.

Fixing to remove the non-deterministic I_S selecting as redundant
from a part of the test dealing with BUG@22864.


mysql-test/suite/rpl/r/rpl_row_create_table.result:
  results updated.
mysql-test/suite/rpl/t/disabled.def:
  rpl_row_create_table is re-enabled.
mysql-test/suite/rpl/t/rpl_row_create_table.test:
  removed a non-deterministic I_S selecting as redundant
  from a part of the test dealing with BUG@22864.

correcting c&p typos in the results

correcting c&p typos in the test

The problem is that cond->fix_fields(thd, 0) breaks
condition(cuts off 'having'). The reason of that is
that NULL valued Item pointer is present in the
middle of Item list and it breaks the Item processing
loop.


mysql-test/r/having.result:
  test case
mysql-test/t/having.test:
  test case
sql/item_cmpfunc.h:
  added ASSERT to make sure that we do not add NULL valued Item pointer
sql/sql_select.cc:
  skip adding an item to condition if Item pointer is NULL.
  skip adding a list to condition if this list is empty.

performance degradation.

Filesort + join cache combination is preferred to full index scan because it
is usually faster. But it's not the case when the index is clustered one.

Now test_if_skip_sort_order function prefers filesort only if index isn't
clustered.

mysql-test/r/innodb_mysql.result:
  Added a test case for the bug#50843.
mysql-test/t/innodb_mysql.test:
  Added a test case for the bug#50843.
sql/sql_select.cc:
  Bug#50843: Filesort used instead of clustered index led to
  performance degradation.
  Now test_if_skip_sort_order function prefers filesort only if index isn't
  clustered.