Fix for panning issue with OpenAL

Pans the sound along a semi circle in front of the listener instead of moving just sideways. This makes it possible to pan a sound slightly to one side, as opposed to the earlier all-or-nothing behavior.

Before, a SoundTransform with a pan that is anything but 0 will play entirely in either the left or right channels. With this fix a pan set to either -1 or 1 is required for this to happen, as is the expected behavior. 

A small test case is available here: https://dl.dropboxusercontent.com/u/32925/Lime_OpenAL_PanTest.zip