avcodec: Add little-endian G726 decoder

Fixes part of Ticket1955
suggested by Roman.

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
avformat: Use G726LE decoder for Sun AU files

fixes ticket #1955 as suggested by Roman.

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>