Avoid stomping of bulk postdata inside the bulk_edit_posts() loop.

Merges [27990] to the 3.8 branch.

props kovshenin.
see [27964], see #27452.


git-svn-id: https://develop.svn.wordpress.org/branches/3.8@27991 602fd350-edb4-49c9-b593-d223f7449a82
3.8.2-RC1


git-svn-id: https://develop.svn.wordpress.org/branches/3.8@27994 602fd350-edb4-49c9-b593-d223f7449a82