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

Same as ".m4a".

.. instead of av_get_bits_per_sample_format().  The SampleFormat enum
value is authoritative.

Replaced all occurrences of g_error() with MPD_ERROR() located in a new header
file 'mpd_error.h'. This macro uses g_critical() to print the error message
and then exits gracefully in contrast to g_error() which would internally call
abort() to produce a core dump.

The macro name is distinctive and allows to find all places with dubious error
handling. The long-term goal is to get rid of MPD_ERROR() altogether. To
facilitate the eventual removal of this macro it was added in a new header
file rather than to an existing header file.

This fixes #2995 and #3007.

According to the mantis bug report 2847, there are several possible
variations of the "album artist" tag:

- "album artist"
- "album_artist"
- "albumartist"

This patch adds support for the latter two.

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

RVA2 tags only store the "gain" value, there is no "peak" attribute.

In libwildmidi 0.2.3, the function WildMidi_SampledSeek() was removed,
without changing the SO name.  This patch adds an autoconf check for
that function.  Fall back to WildMidi_FastSeek() if
WildMidi_SampledSeek() is not available anymore.

libavformat 0.6 does not pass the original URI pointer to the "open"
method, which leads to a crash because MPD was using a dirty hack to
pass a pointer to that method.

This patch switches to av_open_input_stream() with a custom
ByteIOContext class, instead of doing the URI string hack with
av_open_input_file().

Loosely based on a patch from Jasper St. Pierre.

Use the libavformat function av_probe_input_format() to probe the
AVInputFormat, instead of letting av_open_input_file() do it
implicitly.  We will switch to av_open_input_stream() very soon, which
does not have the probing code.

Loosely based on a patch from Jasper St. Pierre.

in some formats, e.g. vorbis, the metadata is stored per-stream.

libavformat 0.6 does not pass the original URI pointer to the "open"
method, which leads to a crash because MPD was using a dirty hack to
pass a pointer to that method.

This patch switches to av_open_input_stream() with a custom
ByteIOContext class, instead of doing the URI string hack with
av_open_input_file().

Loosely based on a patch from Jasper St. Pierre.

Use the libavformat function av_probe_input_format() to probe the
AVInputFormat, instead of letting av_open_input_file() do it
implicitly.  We will switch to av_open_input_stream() very soon, which
does not have the probing code.

Loosely based on a patch from Jasper St. Pierre.

Free the string allocated by decoder_get_uri().

This fixes a theoretical crash, which has never occurred in practice.

Fix a memory leak in some code paths.

We already supported "albumartist", but it seems some folks also use
"album artist" (with a space).

The return value of Player_LoadTitle() is allocated with malloc(), and
must be freed by the caller.

Reuse the function tag_name_parse_i().

Initialize the ov_callbacks struct at compile time.

I'm not sure if mapping "band" to TAG_PERFORMER is correct, but it
might be better than nothing.

Convert if/else/else/... to a loop.

We already supported "albumartist", but it seems some folks also use
"album artist" (with a space).

The return value of Player_LoadTitle() is allocated with malloc(), and
must be freed by the caller.

Added macros with better names: GME_BUFFER_FRAMES, GME_BUFFER_SAMPLES
(the former only used to calculate the latter).

Move into enums.

Pass sizeof(buf) to decoder_data(), not the number of samples (which
is half the size).  At the same time, pass GME_BUF_SIZE to gme_play()
- libgme really wants to get the number of samples, not the number of
stereo frames.  Previously, this plugin had been using only the first
half of the buffer.