ao: print requested audio format on init

Also remove the rather bad/incomplete log calls from ao_alsa and ao_oss.
af: allow filters to return AF_OK, even if format doesn't match

This should allow to make format negotiation much simpler, since it
takes the responsibility to compare actual input and accepted input
formats from the filters. It's also backwards compatible. Filters which
have expensive initialization still can use the old method.
af_surround: fix format negotiation

This did strange things; perhaps caused by the channel layout changes.
af_convert24: fix complicated and incorrect format negotiation

The conversion works for native endian only. The correct check lists
supported format combination explicitly, but is also much simpler.
af_lavrresample: move libavresample setup to separate function

Helps with readability. Also remove the ctx_opt_set_* helper macros and
use av_opt_set_* directly (I think these macros were used because the
lines ended up too long, but this commit removes two indentation levels,
giving more space).
af_lavrresample: reconfigure libavresample only on successful init

If filter initialization fails anyway, we don't need to reconfigure
libavresample.
af_scaletempo: uncrustify

Also do some cosmetic changes, like merging definition and
initialization of local variables.

Remove an annoying debug mp_msg() from af_open(). It just printed the
command line parameters; if this is really needed, it could be added
to af.c instead (similar as to what vf.c does).
Remove sh_audio->samplesize

This member was redundant. sh_audio->sample_format indicates the sample
size already.

The TV code is a bit strange: the redundant sample size was part of the
internal TV interface. Assume it's really redundant and not something
else. The PCM decoder ignores the sample size anyway.
ao_alsa: use correct magic spdif flags

I accidentally copied the AES4/ORIGFS constants from the ALSA headers,
instead of the AES3/FS ones. The difference is probably important.
af_volume: use only one volume setting for all channels

In theory, af_volume could use separate volume levels for each channel.
But this was never used anywhere.

MPlayer implemented something similar before (svn r36498), but kept the
old path for some reason.
gl_hwdec_vdpau: silence warning caused by buggy GL_NV_vdpau_interop spec

VDPAU handles are integers, but for some reasons the VDPAU GL extension
expects them as void*.