Use the existing PcmDither library.

Instead of just adding a rectangular random value before shifting back
to the normal scale, use the existing PcmDither library.

This code is unable to dither.  Until we implement that, let's remove
the code for now.  i386 isn't relevant anymore anyway.

16 bit is not enough for volume calculations.

All callers need this shift, so let's move it to the basic method.

Avoid GLib.

Obsolete, our logging library doesn't ues GLib anymore.

The "mode" of the second ReplayGainFilter was never set, and thus
replay gain was never applied to the new song during cross-fade.

Since opening the PcmVolume object can now fail, this case must be
handled.

Prepare for adding state.

Rename pcm_convert_domain to pcm_domain.  Move it out so we can use it
without depending on the whole PcmConvert library.

Use the SampleTraits template and let the compiler generate a special
case for S32 instead of reusing S24_P32.

Move from PcmClamp().

I've created an elementary input plugin that plays sound from the
soundcard, so you can use MPD to listen to anything connected to the
line-in jack, or to Video4Linux FM radio cards that send audio through
the soundcard.  There has been a small number of posts here in the
past requesting line-in input, so here is a first, simplistic stab at
it.

The patch adds a new sheme, alsa://, which causes mpd to play data
read directly from a souncdard.  It defaults to hw:0,0, but you can
pass any ALSA device name in the URI.  So, using mpc for example:

 mpc add alsa://
 mpc play

will play from device hw:0,0.

To use a diffferent device:

 mpc add alsa://hw:1,0