title: Pip: Specifying minor version
body: <p>In my <code>requirements.txt</code> file I want to specify that my app needs Django version 1.3.x. That is, either 1.3.0, or 1.3.1, or 1.3.2, etc. (When these come out.) But not 1.4, when it comes out.</p>
  
  <p>What's the syntax for this?</p>