Fixes and tweaks for OpenSL.
Use GCC atomics to avoid locking in callback.

Conflicts:
	audio/opensl.c
Use 44.1kHz audio on Android.

Should be toggleable (or use autodetect if present on Android 4.2+).
Fixes audio on Nexus 10 in my test case.
Check for hardware sampling rate automatically.
Merge pull request #260 from Themaister/opensl-upstream

Fixes and tweaks for OpenSL