title: What are all these hidden ('._' prefixed) files that are in my git repo?
body: <p>When I do a 'git status' on my directory, it shows a bunch of untracked files that seem to be duplicates. The only difference is that all have a prefix of <code>._</code>. For example: One of my untracked files that needs to be added would be... <code>app/assets/stylesheets/categories.css</code> and another file would display as <code>app/assets/stylesheets/._categories.css</code>. </p>
  
  <p>Does anyone know what this is all about? There seems to be no good documentation on GitHub.</p>