asserts.
The patch for Bug#21074 replaces acquisition of the global LOCK_open lock
with exclusive locks on table names in such operations ad DROP TABLE
and RENAME TABLE.
Unfortunately, NDB internally assumes that LOCK_open is acquired and
tries to release it.
This dependency should be fixed by a separate (and significant in size)
patch. For now we just satisfy it - after all, the original
goal of the patch for Bug#21074 was to move query_cache_invalidate
outside of the scope of LOCK_open, and we still can do that.

This fixes some failing NDB tests in the runtime tree.