Add/ensure OS X support

[dmcc]

Untested, so maybe already works (at least for subprocess).

[dmcc]

@headdenw has gotten both backends running successfully on OS X 10.8.

[dmcc]

@cdg720 got the test suite to pass on OS 10.9

uname: Darwin redacted 13.4.0 Darwin Kernel Version 13.4.0: Sun Aug 17 19:50:11 PDT 2014; root:xnu-2422.115.4~1/RELEASE_X86_64 x86_64

Please comment if you can test on OS 10.10.