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.

Built from https://develop.svn.wordpress.org/trunk@28113


git-svn-id: http://core.svn.wordpress.org/trunk@27944 1a063a9b-81f0-0310-95a4-ce76da25c4cd