title: how to force installation of xcode
body: <p>I tried to install XCode via AppStore but it fails with the following message:</p>
  
  <pre><code>We could not complete your purchase
  Xcode is already installed on this computer. Choose Software Update from the Apple menu to check for available updates.
  </code></pre>
  
  <p>This might be caused by a previous try via Download from DevelopersCenter - but as that one failed, I tried with the AppStore which is now failing too...</p>
  
  <p>How can I make really remove all from the failed XCode installation to have a retry with the AppStore?</p>
  
  <p>btw. I already did this:</p>
  
  <pre><code>sudo /Developer/Library/uninstall-devtools --mode=all
  </code></pre>
  
  <p>Many thanks!</p>