Ensure edit_post() promotes an auto-draft to draft. Fixes Quick Draft.

For the 3.8 branch. Regression from [27976] that does not affect trunk.

props dd32.
see #27734.


git-svn-id: https://develop.svn.wordpress.org/branches/3.8@28073 602fd350-edb4-49c9-b593-d223f7449a82