title: convert short youtube url to full url
body: <p>Hi all i am looking for a simple way to check if a string equals an url like this:</p>
  
  <pre><code>http://youtu.be/WWQZ046NeUA
  </code></pre>
  
  <p>To convert it to a proper youtube url like this:</p>
  
  <pre><code>http://www.youtube.com/watch?v=WWQZ046NeUA
  </code></pre>
  
  <p>If not to leave it alone, what's the simplest way to do it in php?</p>