title: How to show the diff specific to a named branch in mercurial
body: <p>Assuming I have a named branch foo with two commits a, b:</p>
  
  <pre><code>      a       b       c  
  ------o-------o-------o------- # default
         \          d         e
          ----------o---------o  # branch foo
  </code></pre>
  
  <p>I want to see the diff between a and e (a not included). I could of course use the revision id, but that's not very practical. In git, one can just do git diff master..foo. How can I do the same in hg ?</p>