title: Unicorn / KGIO fails to install on Mountain Lion w/ ruby 1.9.3
body: <p>The main error message is:</p>
  
  <pre><code>checking size of struct RFile in ruby.h,ruby/io.h... *** extconf.rb failed ***
  </code></pre>
  
  <p>kgio successfully installs on ruby 1.9.1, using RVM, but fails on ruby 1.9.3. I'm on Mountain Lion with Xcode + Command Line Tools installed.</p>
  
  <p>Any ideas?</p>