af_asyncts: fix compensation and PTS monotonicity

This patch improves af_asyncts behavior on streams with bogus PTS, which
are either non-monotonic, or contain PTS jitter, and trigger the
non-monotonicity error. With this patch, af_asyncts is able to correct
these streams and avoid the error.

Firstly, it fixes resample compensation calculation by supplying proper
units to avresample_set_compensation (sample count per second instead
of sample count per some arbitrary frame size). Also, the calculation of
the compensation itself is fixed - delta is proportional to an adjustment
of the compensation, not the compensation itself. Ideally, the compensation
should converge to a value that keeps delta at zero.

To be able to deal with sources with PTS jitter even without resampling,
small PTS errors are adjusted, so the output frames do not overlap.

Finally, one more monotonicity check is added.

The FATE reference changes because now there is 8 less samples of
silence because of the pts jitter.

Signed-off-by: Jindřich Makovička <makovick@gmail.com>
