_block_rehash() performance issue.

Drupal instance with over 5000 bean blocks and when a block is saved it calls block_flush_cache() which calls _block_rehash(). The query created by the _block_rehash() continues to show up in the mysqld-slow.log and may have been the catalyst for an outage.

As a result this patch transforms the query produced by the _block_rehash() function.
We’re changing the query from:

SELECT b.*
  FROM 
  block b
 WHERE (( (module = 'block') 
AND (delta = '7') )OR( (module = 'webform') 
AND (delta = 'client-block-268123') )OR( (module = 'webform') 
AND (delta = 'client-block-268129') )OR( (module = 'webform') 
AND (delta = 'client-block-292063') )OR( (module = 'apachesolr_search') 
AND (delta = 'mlt-001') )OR( (module = 'apachesolr_search') 
AND (delta = 'article_related_articles') )OR( (module = 'apachesolr_search') 
AND (delta = 'topic_related_topics')
…

to:

SELECT b.*
FROM.
block b
WHERE (( (module = 'block') 
AND (delta IN  ('7')) )OR( (module = 'webform') 
AND (delta IN  ('client-block-268129', 'client-block-292063')) )OR( (module = 'apachesolr_search')
…