Bug #39939: DROP TABLE/DISCARD TABLESPACE takes long time in buf_LRU_invalidate_tablespace()

This was already fixed in 5.1+; this is a backport to 5.0.

Detailed revision comments:

r2743 | inaam | 2008-10-08 22:18:12 +0300 (Wed, 08 Oct 2008) | 13 lines
branches/5.0:

Backport of r2742 from branches/5.1:

Fix Bug#39939 DROP TABLE/DISCARD TABLESPACE takes long time in
buf_LRU_invalidate_tablespace()

Improve implementation of buf_LRU_invalidate_tablespace by attempting
hash index drop in batches instead of doing it one by one.

Reviewed by: Heikki, Sunny, Marko
Approved by: Heikki