title: vim-flake8 is not working
body: <p>I installed <a href="https://github.com/nvie/vim-flake8">vim-flake8</a> by git cloning it on my Pathogen bundle folder as usual, but when I tried to run the plugin pressing <kbd>F7</kbd> or using <code>:call Flake8()</code> in one Python file I receive the following message:</p>
  
  <blockquote>
    <p>Error detected while processing function Flake8:</p>
    
    <p>line    8:</p>
    
    <p>File flake8 not found. Please install it first.</p>
  </blockquote>
  
  <p>Anyone has some clue about what is going on ?</p>