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

Merges [28073] from the 3.8 branch to the 3.7 branch.

props dd32.
see #27734.


git-svn-id: https://develop.svn.wordpress.org/branches/3.7@28074 602fd350-edb4-49c9-b593-d223f7449a82