Bug#47633 - assert in ha_myisammrg::info during OPTIMIZE
 
   The server crashed on an attempt to optimize a MERGE table with
   non-existent child table.
 
   mysql_admin_table() relied on the table to be successfully open
   if a table object had been allocated.
 
   Changed code to check return value of the open function before
   calling a handler:: function on it.

mysql-test/r/merge.result:
  Backport of revid:ingo.struewing@sun.com-20091223200354-r2uzbdkj2v6yv111
      Bug#47633 - assert in ha_myisammrg::info during OPTIMIZE
      Updated result file.
mysql-test/t/merge.test:
  Backport of revid:ingo.struewing@sun.com-20091223200354-r2uzbdkj2v6yv111
      Bug#47633 - assert in ha_myisammrg::info during OPTIMIZE
      Changed tests to respect changed TEMPORARY MERGE locking (unrelated).
      Changed tests to respect changed CREATE TABLE ... LIKE (unrelated).
      Changed tests to respect that no new tables can be created
      under LOCK TABLE (unrelated).
      Added test for Bug#47633.
  Changed error numbers to symbolic names.
  Added test for child locking for ALTER under LOCK TABLE.
  
  Since Bug 36171 is not pushed yet, not the whole patch has been backported.
mysys/my_delete.c:
  Backport of revid:ingo.struewing@sun.com-20091223200354-r2uzbdkj2v6yv111
      Bug#47633 - assert in ha_myisammrg::info during OPTIMIZE
      Fixed error reporting.
      Fixed indentation.
mysys/my_mmap.c:
  Backport of revid:ingo.struewing@sun.com-20091223200354-r2uzbdkj2v6yv111
      Bug#47633 - assert in ha_myisammrg::info during OPTIMIZE
      Added DBUG.
sql/item_func.cc:
  Backport of revid:ingo.struewing@sun.com-20091223200354-r2uzbdkj2v6yv111
  Added Debug Sync point, required by merge_sync.test.
sql/sql_table.cc:
  Backport of revid:ingo.struewing@sun.com-20091223200354-r2uzbdkj2v6yv111
      Bug#47633 - assert in ha_myisammrg::info during OPTIMIZE
      Do not call handler:: functions if the table was not opened
      successfully.
  Added Debug Sync point, required by merge_sync.test.
storage/myisam/mi_check.c:
  Backport of revid:ingo.struewing@sun.com-20091223200354-r2uzbdkj2v6yv111
      Bug#47633 - assert in ha_myisammrg::info during OPTIMIZE
      Unmap memory before exchanging data files. Needed on Windows.
storage/myisammrg/ha_myisammrg.cc:
  Backport of revid:ingo.struewing@sun.com-20091223200354-r2uzbdkj2v6yv111
  Added Debug Sync point, required by merge_sync.test.
  
  merge_sync.test will be introduced by a patch for Bug 36171,
  which is not pushed yet.