Use only ConfigData.hxx in plugin sources to reduce header
dependencies.

Replaces GLib's GError.

Avoid duplicating the tag.

Hide the definition from C code, to prepare the transition to C++.

Let the function decoder_replay_gain() update
decoder_control::replay_gain_db instead of letting each decoder plugin
take care for that.

These are confusing, and since MixRamp development has ceased, not
useful to anybody.

Pass a callback table to scan_file() and scan_stream(), instead of
returning a tag object.

Add GMutex, GCond attributes which will be used by callers to
conditionally wait on the stream.

Remove the (now-useless) plugin method buffer(), wait on GCond
instead.  Lock the input_stream before each method call.  Do the same
with the playlist plugins.

Rename the "version" struct, because it seems to be a reserved name on
Solaris:

 "src/decoder/mad_decoder_plugin.c", line 550: (enum) tag redeclared: version
 cc: acomp failed for src/decoder/mad_decoder_plugin.c

Be consistent with the rest of MPD, and don't use the non-portable
header "malloc.h".

Adds mixrampdb and mixrampdelay commands.  Reads MIXRAP_START and
MIXRAMP_END tags from FLAC files and overlaps instead of crossfading.

Don't allocate each replay_gain_info object on the heap.  Those
objects who held a pointer now store a full replay_gain_info object.
This reduces the number of allocations and heap fragmentation.

Make it X_decoder_plugin.c.

This function replaces the replay_gain_info parameter for
decoder_data().  This allows the decoder to announce replay gain
changes, instead of having to pass the same object over and over.

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.

Remove the data_time parameter from decoder_data().  This patch
eliminates the timestamp counting in most decoder plugins, because the
MPD core will do it automatically by default.

This patch prepares support for floating point samples (and probably
other formats).  It changes the meaning of the "bits" attribute from a
bit count to a symbolic value.

Let the audio_check library verify the audio format in all (relevant,
i.e. non-hardcoded) plugins.

After we've been hit by Large File Support problems several times in
the past week (which only occur on 32 bit platforms, which I don't
have), this is yet another attempt to fix the issue.

The "off_t" type may change when you enable or disable large file
support on 32 bit platforms.  This caused severe ABI problems within
MPD when we enabled LFS for the first time: two sources included
config.h and sys/types.h in different order, and had different off_t
sizes - leading to memory corruption because of ABI incompatibility.
This patch attempts to get rid of all public "off_t" uses: it removes
"off_t" from the input_stream ABI/API, and switches to GLib's 64 bit
"goffset" type.  This may hurt 32 bit embedded platforms a tiny bit,
but that's not even measurable.

When libid3tag is disabled, the libmad decoder plugin is unable to
identify ID3 frames.  If the file starts with an (unidentified) ID3
frame, it assumes that the file is not a valid MP3 song.  This patch
solves this by adding minimal stubs for the ID3 functions.