Reverting r45058 "(bug 15430) Cancel the upload process and rollback database changes...

Reverting r45058 "(bug 15430) Cancel the upload process and rollback database changes in case no article associated with the file can be created"

Article::doEdit() opens and commits transactions of its own, so the transaction we started earlier will already be committed and cannot be rolled back at this point unless one of two particular failure modes hits (ArticleSave hook aborts or mLatest isn't set). A more general fix needs to be devised...