title: Get a list of changelists that have not been integrated into a particular branch
body: <p>If I have Branch A and Branch B.  Branch B was branched from Branch A.  Periodically, we integrate changes from Branch B back into Branch A.  Is there a p4 command for listing the Branch B changelists that have not yet been integrated into Branch A?  I can think of some reasons that this may not be possible given that a changelist's files is not necessarily limited to a single branch, but I'm hoping for the best here.</p>
  
  <p>I have found this question: <a href="https://stackoverflow.com/questions/3737012/is-it-possible-to-list-the-changelists-that-have-been-integrated-to-a-workspace">Is it possible to list the changelists that have been integrated to a workspace?</a></p>
  
  <p>... which is the opposite of what, I want but makes it clear that there are ways to do this using multiple commands. I can think of a couple of ways to use multiple commands to get what I want, but before I go down that road I'd like to make sure there's no simple way to do this.</p>