Bug 941296 - h.264 platform decoder for OS X. r=cpearce

Implement an h.264 decoder using Apple's VideoToolbox framework.
Based on gstreamer's vtdec because there's very little documentation
for this API beyond the framework's header file.

We provide a stub header for the VideoToolbox framework and load
it dynamically at run time so we can build and run on versions
prior to MacOS X 10.8 where it's not available.

AAC decoding is stubbed to use the BlankDecoderModule's 440A tone.

Reuse the MOZ_APPLEMEDIA define from the mp3 decoder.
Bug 941296 - AAC platform decoder for OS X. r=edwin

WIP Stub out Apple decoder for mpeg audio based on AudioToolbox.
Bug 941296 - Enable FMP4 when APPLEMEDIA is enabled. r=cpearce,ted

This requires moving the MOZ_APPLEMEDIA define. I put it in
alphabetical order with the other platform decoder checks.

Also removes the --disable-apple-media configure switch.
We don't have proper testing for these options, so it's
better not to offer the choice.