Search for OpenAL framework on OSX

if pkg-config does not find OpenAL on OSX, do a manual search for the
OpenAL framework.

references #140
Merge pull request #141 from jin-eld/openal-sx

Search for OpenAL framework on OSX
Merge branch 'master' of https://github.com/Tox/toxic
more fixes
Merge branch 'master' of https://github.com/JFreegman/toxic into groupbot