title: coffeescript not null or undefined behavior
body: <p>so i'm playing around with <a href="http://js2coffee.org/">coffee-script</a> and got this behavior: </p>
  
  <p><code>a?</code> will translate to <code>typeof a !== "undefined" &amp;&amp; a !== null;</code> - that's fine</p>
  
  <p>the problem is if i try the same for <code>a.foo?</code>. this time it translate to <code>a.foo != null;</code>
  the same result i get for <code>a[foo]</code> also. </p>
  
  <p>is there a "fast" way to check if <code>a.foo</code> is not null or undefined like there is with a? </p>