Fix issue357

Fix issue357
Do what the spec says, insane or not:
"
Format 0 (uncompressed) and Format 3 (uncompressed little-endian) are similar. Both encode
uncompressed audio samples. For 8-bit samples, the two formats are identical. For 16-bit
samples, the two formats differ in byte ordering. In Format 0, 16-bit samples are encoded and
decoded according to the native byte ordering of the platform on which the encoder and Flash
Player, respectively, are running. In Format 3, 16-bit samples are always encoded in little-endian
order (least significant byte first), and are byte-swapped if necessary in Flash Player before
playback. Format 0 is clearly disadvantageous because it introduces a playback platform
dependency. For 16-bit samples, Format 3 is highly preferable to Format 0 for SWF version 4
or later.
"

Originally committed as revision 12184 to svn://svn.ffmpeg.org/ffmpeg/trunk