AAC->M4A/MP3 patches at github - one more time

[dinkypumpkin]

For anyone keeping score, I've reposted patched code at github for anyone who wishes to test AAC->M4A or AAC->MP3 conversion.  

I'm now tracking Shevek's code in its own branch:

https://github.com/dinkypumpkin/get_iplayer/blob/aactom4a-shevek/get_iplayer

This branch contains Shevek's FIRST patch with 2 passes by ffmpeg: FLV->AAC->M4A.  It worked OK for me.

And I'm now tracking my code to support AAC->MP3 transcoding in a separate branch (includes Shevek's code):

https://github.com/dinkypumpkin/get_iplayer/blob/aactomp3-shevek/get_iplayer

Once solidified, I'll merge the two.  If anyone else wants to contribute to the above, I'm happy to coordinate submissions from the list and post to github.  If you find anything actually broken in the code I've posted, please reply to this thread.