title: vim says "No mouse support", but only when I run git commit
body: <p>I like using the mouse with vim, so I have mouse support enabled in my <code>.vimrc</code>. This works just fine most everywhere, but whenever I run <code>git commit</code> on a specific server (Appa), I get an error message:</p>
  
  <pre><code>[tswett@appa git]$ git commit
  Error detected while processing /home/tswett/.vimrc:
  line    1:
  E538: No mouse support: mouse=a
  Press ENTER or type command to continue
  Aborting commit due to empty commit message.
  [tswett@appa git]$
  </code></pre>
  
  <p>I end up with a vim session that has no mouse support and no syntax highlighting.</p>
  
  <p>If I run <code>git commit</code> on a different server, or on my local machine, I do have mouse support and syntax highlighting. Likewise, whenever I use vim to edit anything <em>else</em> on Appa, I have mouse support and syntax highlighting. If I remove the <code>set mouse=a</code> line from <code>.vimrc</code> and <em>then</em> run <code>git commit</code> on Appa, I no longer get an error message, but I also don't get syntax highlighting, either.</p>
  
  <p>How can I get vim, <code>git commit</code>, and Appa to all play nice with each other?</p>
  
  <p>Appa's operating system is RHEL 6.3 (Santiago); Appa's vim is version 7.2; and Appa's git is version 1.7.1. Here's my <code>.vimrc</code> (identical across all machines): <a href="https://github.com/tswett/setup/blob/c84c8908a04a1d925d90da3da4f2fc83bf56172b/.vimrc" rel="noreferrer">https://github.com/tswett/setup/blob/c84c8908a04a1d925d90da3da4f2fc83bf56172b/.vimrc</a></p>