get_bits: add get_bits_le()

Signed-off-by: Paul B Mahol <onemda@gmail.com>
ADPCM IMA WAV 2, 3 and 5 bits decoder

Signed-off-by: Paul B Mahol <onemda@gmail.com>
avformat/avidec: Fix incorrect detection of badly interleaved avi

The method guess_ni_flag needs to divide timestamps in the index
by sample_size if it is set in order to compare different streams correctly.

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