title: Check whether pathogen is installed in vimrc
body: <p>I would like to check in <code>.vimrc</code> whether pathogen is present, and call <code>pathogen#infect</code> if it is.</p>
  
  <p>This obviously works:</p>
  
  <pre><code>call pathogen#infect()
  </code></pre>
  
  <p>So I'm confident pathogen is properly installed.</p>
  
  <p>But this does not load pathogen:</p>
  
  <pre><code>if exists("*pathogen#infect")
      call pathogen#infect()
  endif
  </code></pre>
  
  <p>Neither does this:</p>
  
  <pre><code>if exists("g:loaded_pathogen")
      call pathogen#infect()
  endif
  </code></pre>
  
  <p>What am I missing?</p>