------------------------------------------------------------------------
  r4004 | marko | 2009-01-20 16:19:00 +0200 (Tue, 20 Jan 2009) | 12 lines

  branches/5.1: Merge r4003 from branches/5.0:

  rec_set_nth_field(): When the field already is SQL null,
  do nothing when it is being changed to SQL null. (Bug #41571)

  Normally, MySQL does not pass "do-nothing" updates to the storage engine.
  When it does and a column of an InnoDB table that is in ROW_FORMAT=COMPACT
  is being updated from NULL to NULL, the InnoDB buffer pool will be corrupted
  without this fix.

  rb://81 approved by Heikki Tuuri
  ------------------------------------------------------------------------
  r4005 | marko | 2009-01-20 16:22:36 +0200 (Tue, 20 Jan 2009) | 8 lines

  branches/5.1: lock_is_table_exclusive(): Acquire kernel_mutex before
  accessing table->locks and release kernel_mutex before returning from
  the function.  This fixes a portential race condition in the
  "commit every 10,000 rows" in ALTER TABLE, CREATE INDEX, DROP INDEX,
  and OPTIMIZE TABLE. (Bug #42152)

  rb://80 approved by Heikki Tuuri
  ------------------------------------------------------------------------