Fix this by passing the HA_EXTRA_PREPARE_FOR_DELETE onto the newly added or about to be dropped partitions
so they have an opportunity to close their OS file handle.


client/mysqltest.c:
  prevent positive find of pattern when pattern has zero length (this has nothing to do with this bug fix)
sql/ha_partition.cc:
  initialize m_new_file to NULL
  call new function prepare_for_delete for the HA_EXTRA_PREPARE_FOR_DELETE operation
  inside prepare_for_delete, loop over m_new_file and m_reorged_file if they are non-NULL
sql/ha_partition.h:
  added decl for new prepare_for_delete function