title: Git: Merge old commit into current head version
body: <p>Got a file that has two commits of interest, both on the <code>Master</code> branch, both only modifying a single file <code>foo</code>: a previous commit <code>AA</code>, and the current version in <code>HEAD</code>. I would like to merge the two versions of the file, keeping bits of both, into <code>HEAD</code> on <code>Master</code>.</p>
  
  <p>I did the simplest thing that I thought would work: </p>
  
  <pre><code>git checkout -b merge-purgatory AA
  git commit -m "pulled foo back from previous commit for merging into HEAD."
  git checkout master
  git merge merge-purgatory
  </code></pre>
  
  <p>Which simply overwrites the current <code>HEAD</code> version of <code>foo</code> with <code>AA</code> version.
  Tried the more verbose <code>git checkout -m</code> as well, same result: a dumb overwrite.</p>
  
  <p>How do I force git to treat the <code>AA</code> version of <code>foo</code> as a conflicting merge with the current <code>HEAD</code> version?</p>