Partially revert [24460] and only flush insert_id on the next insert or replace query, as we had been doing before.

Merges [24494] to the 3.5 branch.



git-svn-id: http://core.svn.wordpress.org/branches/3.5@24495 1a063a9b-81f0-0310-95a4-ce76da25c4cd