title: Upgrading Xcode issue
body: <p>I am currently working with Xcode 4.5.2 and I'd like to upgrade it to version 4.6. Will installing the new version completely replace the previous one? If so, is it possible to just "extend" your current version and keep the SDKs you already have? I wouldn't like to lose the compatibility with my current projects...</p>
  
  <p>Thanks!</p>