gst/qtdemux/qtdemux.c: Figure out the real audio type in mp4a boxes by parsing the optional descriptors in the option...

Original commit message from CVS:
* gst/qtdemux/qtdemux.c: (qtdemux_parse), (qtdemux_parse_trak),
(gst_qtdemux_handle_esds):
Figure out the real audio type in mp4a boxes by parsing the
optional descriptors in the optional esds box. Promote the
default AAC to mp3 when indicated. Fixes #330632.