Additional fix for INSERT DELAYED with subselect.
Originally detected in 5.1, but 5.0 could also be affected.
The user thread creates a dummy table object,
which is not included in the lock. The 'real' table is
opened and locked by the 'delayed' system thread.
The dummy object is now marked as not locked and this is
tested in mysql_lock_have_duplicate().


sql/lock.cc:
  BUG#5390 - problems with merge tables
  Additional fix for INSERT DELAYED with subselect.
  The user thread creates a dummy table object,
  which is not included in the lock.
  Changed to safer asserts.
sql/sql_insert.cc:
  BUG#5390 - problems with merge tables
  Marked the dummy table object as not being
  included in the lock.