title: Xcode stops working after set "xcode-select -switch"
body: <p>OMG, what I've done? </p>
  
  <p>Couple of days ago, I tried using macport to install something, because I'm using Xcode 4.3 and the command-line tool hadn't been installed by the time, macport wouldn't work. So I followed some guide to get command-line tool installed, then I used following command:</p>
  
  <pre><code>sudo xcode-select -switch /Applications/Xcode.app/
  </code></pre>
  
  <p>which I think screwed everything except macport: now, in Xcode, even a simple single-view iOS project won't be compiled, it says "UIKit/UIKit.h not found".</p>
  
  <p>Does anyone know how to correct this? I don't want to re-install the gigantic Xcode again, gotta do some iOS project tonight, help!</p>