Updating CMake for Summer Project Week 2013

This change is based on the very helpful suggestions of
Jean-Christophe Fillion-Robin:
It is now good to use project() statement in your extension, and you
don't have to use if(NOT Slicer_SOURCE) anymore.
Fixing PixelID usage for newer SimpleITK

The enum type needs to be used instead of just an int.
Copying in latest itkBinShrinkImageFilter and Scanline iterators