Mac Core audio - enabled and with echo cancellation on by default.

Manual application of jitsi commit https://github.com/jitsi/libjitsi/commit/e0a583630cc2ab0011aeea84f3bb1c64845eb20f - we already have (updated) DeviceSystem.java changes, so just manually apply the MacCoreaudio one-line change.
Updates AEC for CoreAudio using webrtc library, recompiled with latest webrtc, was crashing when running from source with unresolved reference "___sincos_stret". Adds some basic instructions for compiling.

Conflicts:
	src/native/build.xml
Removes tab char.

Conflicts:
	src/native/build.xml