audio: Implemented capture support for Mac OS X CoreAudio.

I don't know what iOS wants yet, so this code might work there, too...?

src/audio/coreaudio/SDL_coreaudio.h

@@ -50,6 +50,7 @@ struct SDL_PrivateAudioData
     UInt32 bufferSize;
 #if MACOSX_COREAUDIO
     AudioDeviceID deviceID;
+    AudioBufferList captureBufferList;
 #endif
 };