title: git remove files when undoing failed merge
body: <p>I have merged <code>master</code> into my <code>bugXY</code> branch, and needed to merge a file. But <code>git mergetool</code> failed (my noob fault, I guess), and even though I aborted the merge it left me with a dirty working directory but not in need-to-merge state. I would like to repeat the merge command, but I can't due to some new files left by the merge.</p>
  
  <p>How can I undo the merge (I didn't commit anything) and get exactly the working directory from before?</p>
  
  <p>What I did:</p>
  
  <pre><code>&gt; git checkout bugXY
  On branch "bugXY" - nothing to commit
  &gt; git merge master
  [modifying and adding lots of files]
  one file with conflict
  On branch "bugXY|MERGING"
  &gt; git mergetool
  You could use a, b or c
  merged // didn't work, no GUI appeared and I did not do anything
  do you want to remove, commit or abort?
  &gt; abort // Hu, what happened?
  On branch "bugXY" // no MERGING any more???
  </code></pre>
  
  <p>Oops, what have I done? A repeated <code>git merge</code> does not work, I have changed (and staged) files in my working directory now. OK, undo it. I tried:</p>
  
  <pre><code>&gt; git reset --hard HEAD
  </code></pre>
  
  <p>and</p>
  
  <pre><code>&gt; git checkout bugXY
  </code></pre>
  
  <p>Now nothing is staged any more, but I still have a bunch of <em>untracked working tree files</em> which hinder me to <code>git merge</code> again ("would be overwritten, please [re]move them"). How can I do that? I guess <code>rm path/to/file.php</code> for each of them would work, but there are a lot of them...</p>