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

Reverts [27990] which did not fix it for authors and comment/ping status.

props dd32, DrewAPicture.
fixes #27792.


git-svn-id: https://develop.svn.wordpress.org/trunk@28113 602fd350-edb4-49c9-b593-d223f7449a82