Don't call _mi_decrement_open_count() for mi_extra(HA_EXTRA_PREPARE_FOR_DROP).
This ensures that if we empty the key cache and a drop table fails later, the index will be automaticly rebuilt

storage/maria/ma_extra.c:
  Don't call _ma_decrement_open_count() for ma_extra(HA_EXTRA_PREPARE_FOR_DROP).
  This ensures that if we empty the key cache and a drop table fails later, the index will be automaticly rebuilt
storage/maria/ma_locking.c:
  Simple optimization: Don't call maria_lock_database() if locking is disabled
storage/myisam/mi_extra.c:
  Don't call _mi_decrement_open_count() for mi_extra(HA_EXTRA_PREPARE_FOR_DROP).
  Simplify code to remove if