title: invalid cast exception on int to double
body: <p>Maybe I'm crazy, but I thought this was a valid cast:</p>
  
  <pre><code>(new int[]{1,2,3,4,5}).Cast&lt;double&gt;()
  </code></pre>
  
  <p>Why is LinqPad throwing a</p>
  
  <blockquote>
    <p>InvalidCastException: Specified cast is not valid.</p>
  </blockquote>
  
  <p>?</p>