Make clean_post_cache child cleaning optional

[arnee]

clean_post_cache() makes a MySQL query in every call to clean the cache for child posts. This should be optional if the caller knows that there are no child posts or they're not cached.

Background: I need to query all posts have to clean the post cache to stay within the memory limits. Before 2.5 this was fine with clean_post_cache, but since the update the php execution time increased extremely because of this additional db query.

[arnee]

New argument $recursive (true by default)

[ryan]

Milestone 2.5.2 deleted

[nacin]

We fixed this a while ago, thank god. This was nasty.