1. Restore the rest of Python IDLE setup.py Rev 1.4 (Python SF 634078)

(Loewis) which uses 'SRCDIR' (if available) in package dir path.
2. Merge Python IDLE setup.py Rev 1.5 (Loewis) to allow installation
   from the build directory. IDLEfork SF Patch 668998 (Loewis)