move OpenAL helper functions to AL object

Noticed your comment https://github.com/kripken/emscripten/pull/1493#issuecomment-22518283 and realized I had left the helper functions I added during the buffer work months ago out in the global space.

This commit moves them all onto the AL object.

Ran browser.test_openal_playback and browser.test_openal_buffers.