REBUILD PARTITION under LOCK TABLE

Collapsed patch including updates from the reviews.

In case of failure in ALTER ... PARTITION under LOCK TABLE
the server could crash, due to it had modified the locked
table object, which was not reverted in case of failure,
resulting in a bad table definition used after the failed
command.

Solved by instead of altering the locked table object and
its partition_info struct, creating an internal temporary
intermediate table object used for altering,
just like the non partitioned mysql_alter_table.
So if an error occur before the alter operation is complete,
the original table is not modified at all.
But if the alter operation have succeeded so far that it
must be completed as whole,
the table is properly closed and reopened.
(The completion on failure is done by the ddl_log.)

mysql-test/suite/parts/inc/partition_fail.inc:
  Added tests under LOCK TABLE
mysql-test/suite/parts/r/partition_debug_innodb.result:
  Updated results
mysql-test/suite/parts/r/partition_debug_myisam.result:
  Updated results
mysql-test/suite/parts/r/partition_special_innodb.result:
  updated result
mysql-test/suite/parts/t/partition_special_innodb.test:
  changing comment, since this patch also fixes this.
sql/sql_partition.cc:
  Added TODO, to use DBUG_SUICIDE() instead of abort()
  to avoid core-files on expected crashes.
  Removed unused arguments to fast_end_partition.
  Opening a intermediate table in prep_alter_part_table, instead of altering
  (a possible locked) normally opened table.
  That way we do not have to do anything more than close
  the intermediate table on error,
  leaving the ordinary table opened and locked.
  Also making sure that the intermediate table are
  closed/destroyed on failure. If no error occur
  it is later destroyed in the end of fast_alter_partition_table.
  Added ha_external_lock to make sure MyISAM flushed the index file
  after copying the partitions.
  This also leads to removal of the special close and removal from
  the table cache for other instances of the table.
sql/sql_partition.h:
  Changed the arguments for prep_alter_part_table and
  fast_alter_partition_table to use an intermediate table
  instead of altering a (possibly locked) normal table.
sql/sql_table.cc:
  Using an intermediate table created in prep_alter_part_table
  to be used in fast_alter_partition_table, also closing/destroying
  it on failure.