Fix SDL Web Audio to work on Safari 6.0.5. That browser does not implement the AudioBufferSourceNode.start() method, but only has the older .noteOn() method, and the audio ctors don't come out as functions, but strongly typed ctor objects.
Fix OpenAL library to work with old Web Audio API syntax that exists in Safari 6.0.5 at least.
Make tests/openal_playback.cpp compilable outside the test runner.
Fix typo in comment.
Merge pull request #2225 from juj/safari_webaudio

Safari 6.0.5 webaudio fixes in SDL and OpenAL library.