Adds pip, homebrew and builtin satisfier for initial OS X support.

The 'builtin' satisfier only supports OS X at the moment. If there is not any other OS that ships with built-in libraries, one could probably just rename the module to a more OS X specific name.

Everything was tested on OS X Mavericks (10.9) successful.

UHD and gnuradio still have some minor build issues on OS X, especially if they are not compiled with GCC, but these are things that have to be fixed upstream.