title: Detect creating of branches or bookmarks in HG
body: <p>Is it possible to detect if a commit creates a new bookmark or branch via hooks in .hgrc?</p>
  
  <p>I've tried to see if I can find out using hg log, but it just shows on what branch/bookmark the commit has been created: <a href="http://hgbook.red-bean.com/read/customizing-the-output-of-mercurial.html" rel="nofollow">http://hgbook.red-bean.com/read/customizing-the-output-of-mercurial.html</a></p>
  
  <p>There don't seem to be hooks for it: <a href="http://hgbook.red-bean.com/read/handling-repository-events-with-hooks.html" rel="nofollow">http://hgbook.red-bean.com/read/handling-repository-events-with-hooks.html</a></p>
  
  <p>It would make sense I suppose that there isn't a hook for it, because it is also not possible to make a commit which is 'just' the creation of the branch indicating branches/bookmarks only exists when added to a specific commit.</p>
  
  <p>I figured I could check hg branches and hg bookmarks before and after each commit and determine which are removed and added, but is there a cleaner way for detecting branch/bookmark adds/removes?</p>