Revert "remove unused variable in Audio"

This reverts commit bbdd601855c4ce380389c3154954d51ce64e4872.
don't go looking for GLM twice, check the cache
Merge pull request #372 from birarda/master

refactor FindGLM to not check twice, revert the previous audio change
reversed gyro for head (didn't know the headset was on backwards :)
Merge remote-tracking branch 'upstream/master'