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

Merges [28113] to the 3.7 branch.

Reverts [27992] which did not fix it for authors and comment/ping status.

props dd32, DrewAPicture.
fixes #27792.

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git-svn-id: http://core.svn.wordpress.org/branches/3.7@27946 1a063a9b-81f0-0310-95a4-ce76da25c4cd