Makefile compatible with OS X

The Makefile now detects whether OS X (Darwin) is being used, and changes the
extension suffix accordingly from .so to .dylib. On current Apple hardware,
i386 architecture is no longer applicable, so it is removed from the build.
Correction previous commit: OS X Makefile

Only the ARCHLIBS flag is needed, OS X Python uses .so suffix anyway.
Change ARCHFLAGS environment variable in setup.py

Instead of using the Makefile, changed ARCHFLAGS in setup.py
Remove registration.so with make clean
Merge pull request #4 from blootsvoets/scrum

Makefile compatible with OS X