title: Using vimdiff with a different .vimrc?
body: <p>I've been using Vim now for most of my editing for the last week or so and I'm loving the experience.  However I have an issue.</p>
  
  <p>I've setup my <code>.vimrc</code>file with <code>NERD_tree</code> and a few other goodies.  This works well for when I'm coding.  However on occasion I use <code>vimdiff</code> via Git and this causes some problems.  I don't need <code>NERD_Tree</code> open when I do this or many of the other things I've setup in my <code>.vimrc</code> file.</p>
  
  <p>Here's my question.  Is there a way to check what is calling my .vimrc file and have it execute different code depending on the caller?  Specifically how do I test to see if <code>vimdiff</code> is the caller?  Or am I going about this entirely the wrong way?</p>