title: TeamCity - clean checkout
body: <p>Is it possible to perform "Clean all files in the checkout directory before the build" except of two folders?</p>
  
  <p>I want to mark two folders (which are created during the builds) as "not for cleaning".
  To be more specific, I'm using Unity3d to build an app and during the building process, Unity3d creates two folders: Library + Temp.
  I would like to keep those folders in order to speedup the next build (Unity3d will use the Library folder as cache).</p>
  
  <p>Any way to do it?</p>