title: link_to() generates route successfully, but clicking on that link results in a 404
body: <p>I've set a <a href="http://www.dur.ac.uk/trevelyan.alumni/" rel="nofollow noreferrer">website</a> up. If I try and click on a link such as <a href="http://www.dur.ac.uk/trevelyan.alumni/register" rel="nofollow noreferrer">register</a> I get the following error:</p>
  
  <pre><code>404 | Not Found | sfError404Exception
  Empty module and/or action after parsing the URL 
      "/trevelyan.alumni/register" (/).
  </code></pre>
  
  <p>The links are generated using </p>
  
  <pre><code>&lt;?php 
      print link_to( 'Register', 'register/index' ); 
  ?&gt;
  </code></pre>
  
  <p>And I have a 'register' module in apps/frontend/modules/register.</p>
  
  <p>I'm quite new to Symfony, any help is appreciated!</p>
  
  <hr>
  
  <p>routing.yml:</p>
  
  <pre><code># default rules
  homepage:
    url:   /
    param: { module: home, action: index }
  
  default_index:
    url:   /:module
    param: { action: index }
  
  default:
    url:   /trevelyan.alumni/:module/:action/*
  </code></pre>