title: Using Flask-Babel with virtualenv fails
body: <p>I have Flask, Babel and Flask-Babel installed in the global packages. 
  When running python and I type this, no error</p>
  
  <pre><code>&gt;&gt;&gt; from flaskext.babel import Babel
  &gt;&gt;&gt;
  </code></pre>
  
  <p>With a virtual environment, starting python and typing the same command I see</p>
  
  <pre><code>&gt;&gt;&gt; from flaskext.babel import Babel
  Traceback (most recent call last):
    File "&lt;stdin&gt;", line 1, in &lt;module&gt;
  ImportError: No module named flaskext.babel
  &gt;&gt;&gt;
  </code></pre>
  
  <p>The problem is that I'm using Ninja-IDE and I'm apparently forced to use a virtualenv. I don't mind as long as it doesn't break Flask packing system.</p>