Fix swig-python compilation failure on 10.9

As others have found [1], trying to compile the python swig bindings on Mac OS 10.8/10.9 results in the 
error “Unrecognized option -F/usr/local/Frameworks” because CPPFLAGS gets passed through directly to 
swig which does not understand the -F option for frameworks.

Here is a patch to the build to strip CPPFLAGS of two flags that swig does not know about.

[1] https://github.com/Homebrew/homebrew/issues/23993

Original issue reported by andrewdotn