Replacing GLib macros.

Prepare to migrate away from GLib.  Currently, we're still using GLib
as a backend.

Replaces GLib's GError.

DSD-over-USB should not be a MPD core format, because it is not a
"natural" format; it is just a temnporary over-the-wire format.  This
format has been implemented in pcm_export, and does not need to be
supported by pcm_convert.

For 32 bit DSD-over-USB support.

Prepare for removing SAMPLE_FORMAT_DSD_OVER_USB.

For simplicity, the MPD core should not have to deal with packing.  It
is rarely used, and those plugins that need it should use the
pcm_export library instead.

Converts padded 24 bit samples to packed 24 bit samples.  Will replace
the packed S24 sample format, which is not used internally.

Improving oss_reopen() by using the very same value that was used
initially.

Don't use audio_format.reverse_endian.

This format is unused since the DSDIFF decoder plugin now reverses the
bit order.

Make sure we get a UTF-8 encoded string.

Basic support for Direct Stream Digital.  No conversion yet, and no
decoder/output plugin support.

Support for conversion from float to 16, 24 and 32 bit integer
samples.

Pass audio_output objects around instead of void pointers.  This will
give some more control to the plugin, and prepares for non-blocking
audio outputs.

Move the "extern" declarations from output_list.c, for more type
safety.

See code comment.

According to the Solaris dsp manpage, AFMT_S24_PACKED is
little-endian:

 http://download.oracle.com/docs/cd/E19963-01/821-1475/6nmf5baot/index.html

The Minix soundcard.h header says the same.

Remove trailing whitespace found by this command:
find -name '*.[ch]' | xargs grep "[[:space:]]$"