title: diff a directory recursively, ignoring all binary files
body: <p>Working on a Fedora Constantine box. I am looking to <code>diff</code> two directories recursively to check for source changes. Due to the setup of the project (prior to my own engagement with said project! <em>sigh</em>), the directories contain both source and binaries, as well as large binary datasets. While diffing eventually works on these directories, it would take perhaps twenty seconds if I could ignore the binary files.</p>
  
  <p>As far as I understand, diff does not have an 'ignore binary file' mode, but does have an ignore argument which will ignore regular expression <strong>within</strong> a file. I don't know what to write there to ignore binary files, regardless of extension.</p>
  
  <p>I'm using the following command, but it does not ignore binary files. Does anyone know how to modify this command to do this?</p>
  
  <pre><code>diff -rq dir1 dir2
  </code></pre>