Simple (up-rounding) integer division is good enough.  We're casting
the result back to an integer anyway.

Clean up tag and replay_gain_info there.

The cue sheet embedded in a flac file doen't contain any information
about track titles and similar.  There are three possibilities: Use an
external cue sheet that includes these information, use a tag CUESHEET
with a cue sheet including these information or use tags.  I think the
latter is the best option and is already used by other projects.

This updates the copyright header to all be the same, which is
pretty much an update of where to mail request for a copy of the GPL
and the years of the MPD project. This also puts all committers under
'The Music Player Project' umbrella. These entries should go
individually in the AUTHORS file, for consistancy.

Free the tag object when it turns out to be empty.  This simplifies
several functions and APIs.

Renamed types, functions, variables.

Use G_GNUC_UNUSED instead of mpd_unused (which has already been
removed).

SEEK_SET is defined by unistd.h.  Explicitly include it.

Refuse to play audio formats which are not supported by MPD.

Define the special value "-1" as "unknown size".  Previously, there
was no indicator for streams with unknown size, which might confuse
some decoders.

The stream_decode() and file_decode() methods returned a boolean,
indicating whether they were able to decode the song.  This is
redundant, since we already know that: if decoder_initialized() has
been called (and dc.state==DECODE), the plugin succeeded.  Change both
methods to return void.

Renamed functions and variables.

Instead of checking the stream_types bit set, we can simply check
whether the methods stream_decode() and file_decode() are implemented.

Ogg and ffmpeg detection was disabled when the stream was not
seekable, because the detection was too expensive.  Since the curl
input stream can now rewind the stream cheaply, we can re-enable
detection on streams.

Don't pass the "seekable" flag with every decoder_data() invocation.
Since that flag won't change within the file, it is enough to pass it
to decoder_initialized() once per file.

The strings were constant, but the pointers weren't.  C syntax is
somewhat tricky..

All decoder_plugin structs are initialized at compile time, and must
never change.

Again, I forgot to adapt oggflac to the new API (struct input_stream,
bool return values).

Don't return 0/-1 on success/error, but true/false.  Instead of int,
use bool for storing flags.

For boolean values and success flags, use bool instead of integer (1/0
for true/false, 0/-1 for success/failure).

Renamed all functions and variables.

These plugins are not input plugins, they are decoder plugins.  No
CamelCase in the directory name.

Don't compile the sources of disabled decoder plugins at all, and
don't attempt to register these.

The last bit of CamelCase in audio_format.h.  Additionally, rename a
bunch of local variables.

"bool" should be used in C99 programs for boolean values.

The old struct initializers are error prone and don't allow moving
elements around.  Since we are going to overhaul some of the APIs
soon, it's easier to have all implementations use C99 initializers.

There is still a lot of duplicated code in flac_plugin.c and
oggflac_plugin.c.  Move code from flac_plugin.c to _flac_common.c, and
use the new function flac_common_write() also in oggflac_plugin.c,
porting lots of optimizations over to it.

The inline function audio_format_sample_size() calculates how many
bytes each sample consumes.  This function already takes into account
that 24 bit samples are 4 bytes long, not 3.

Fix lots of "unused parameter" warnings in the OggFLAC decoder
plugin.  Not sure if anybody uses it anymore, since newer libflac
obsoletes it.

During the tag library refactoring, the shout plugin was disabled, and
I forgot about adapting it to the new API.  Apply the same fixes to
the oggflac decoder plugin.

It was possible for the decoder thread to go into an endless loop
(flac and oggflac decoders): when a "STOP" command arrived, the Read()
callback would return 0, but the EOF() callback returned false.  Fix:
when decoder_get_command()!=NONE, return EOF==true.

The code said "decoder_command==STOP" because that was a conversion
from the old "dc->stop" test.  As we can now check for all commands in
one test, we can simply rewrite that to decoder_command!=NONE.

On our way to stabilize the decoder API, we will one day remove the
input stream functions.  The most basic function, read() will be
provided by decoder_api.h with this patch.  It already contains a loop
(still with manual polling), error/eof handling and decoder command
checks.  This kind of code used to be duplicated in all decoder
plugins.