* modules/audio_filter/resampler/bandlimited.[ch]: new high-quality
   bandlimited interpolation resampler.
   It is not yet enabled by default because it requires a bit more works
   (not fully stable yet because of buffer overflows under certain conditions).

* src/audio_output/input.c: the resamplers are now always active (expcept
   in spdif mode).

* modules/audio_filter/resampler/*: modified the resampler to return the
   input buffer when no resampling is needed.