title: Pull-Request for only certain files/commits
body: <p>I have a repository that is forked from <a href="http://www.github.com/">GitHub</a> that has a few modifications made to it. However, in a certain commit, a few files were changed that I want to submit a pull-request for, leaving the other modified files out of the request.</p>
  
  <p>Do pull requests merge <em>all</em> commits, or do I need to do something special to isolate this commit?</p>