Invoke decoder_initialized() in the libFLAC metadata callback.  This
merges code from the FLAC and the OggFLAC decoder plugin into the
common library.

Make it X_decoder_plugin.c.

This patch changes the following decoder plugins to implement
stream_tag() instead of tag_dup():

 faad, ffmpeg, mad, modplug, mp4ff, mpcdec, oggflac

This simplifies their code, because they do not need to take care of
opening/closing the stream.

Support deprecated MIME types such as "audio/x-ogg".  Support new
types such as "audio/flac".

Remove the audio_format attribute, add "frame_size" instead.  The
audio_format initialization and check is moved both to
flac_data_get_audio_format().

Use the sample rate stored in the stream_info struct instead of the
audio_format struct.

Don't update a float timestamp, this will make imprecisions add up
after a while.  We already have the number of the current frame, let's
just calculate the float timestamp from that for every decoder_data()
command.  For this, we need to add the attribute "first_frame", for
CUE sheet songs.

Removed the "bit_rate" attribute from the flac_data struct.  Pass the
number of bytes since the last call to flac_common_write(), and let
it calculate the bit rate.

We don't want to work with floating point values if possible.  Get the
integer number of frames from the FLAC__StreamMetadata_StreamInfo
object, and convert it into a float duration on demand.  This patch
adds a check if the STREAMINFO packet has been received yet.

Allow those plugins to open large files on 32 bit platforms.

We need this for more exact end-of-subsong detection for CUE files.

The oggflac plugin has been completely broken for quite a while and
nobody has noticed - maybe we should remove it?

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.