title: Determine at which commit a file entered the master branch in git
body: <p>I'm experimenting with using Git as a CMS for a website because it tracks author information, revisions, and when it was added to the repository.  The problem I'm having is that we want to use branches to track future/not-published content while it's being worked on by several people.  I can't find a sure fire way to determine when an article/file gets added to the master branch so that date can be used as the "published" date instead of the date it was originally added.</p>
  
  <p>Any ideas on how this could be done?</p>