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

dc.error wasn't updated when the input stream failed to initialize.

Renamed variables and functions.

If an input stream provides tags (e.g. from an icecast server), send
them in the decoder_data() and decoder_tag() methods.  Removed the
according code from the mp3 and oggvorbis plugins - decoders shouldn't
have to care about stream tags.

This patch also adds the missing decoder_tag() invocation to the mp3
plugin.

The try_decode() method may have read some data from the stream, which
is now lost.  To make this data available to other methods, get it
back by rewinding the input stream after each try_decode() invocation.

The ogg and wavpack plugins did this manually and inconsistently; this
code can now be removed.

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.

Rename all functions to the new prefix.

No CamelCase in the file name.  The output_buffer struct is going to
be renamed to music_pipe.  There are so many buffer levels in MPD, and
calling this one "output buffer" is wrong, because it's not the last
buffer before the music reaches the output devices.

The decoder_plugin structs must never change.  Don't work with
non-const pointers.

Nearly all mapper functions can fail and will then return NULL.  Add
checks to all callers.

http://xkcd.com/292/

If nobody sent a command, the player isn't waiting for the decoder.
Don't wake it up.

The player should always be woken up when the decoder quits.

Eliminate one goto in decodeStart() by moving some cleanup to
decoder_task().

switch looks much nicer than if/elseif/... and gcc generates nice
warnings when a new command is added to the enum.

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

A decoder_flush() invocation was missing in the FLAC plugin, resulting
in casual assertion failures due to a wrong assumption about the last
chunk's audio format.  It's much easier to remove that decoder_flush()
function and make the decoder thread call ob_flush().

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.

There was only one user of pathcpy_trunc(), which can be eliminated.

Provide a struct type which can be forward-declared.  The typedef
InputStream is deprecated now.

Wake up the player as soon as the decoder thread has entered its loop.
This fixes a dead lock when the input is blocking.

The mapper library maps directory and song objects to file system
paths.  With this central library, the code mixture in path.c should
be cleaned up, and we will be able to add neat features like aliasing.

The runtime check suggests that the author has somehow thought
song_get_url(NULL) might be valid.  It should not be.  Replace it with
an assertion.

CamelCase is ugly...  rename all functions.

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

Again, a data type which can be forward-declared.

Why have a "_func" prefix on all method names?  Also don't typedef the
methods, there is no advantage in that.

There was a known deadlocking bug in the notify library: when the
other thread set notify->pending after the according check in
notify_wait(), the latter thread was deadlocked.  Resolve this by
synchronizing all accesses to notify->pending with the notify object's
mutex.  Since notify_signal_sync() was never used, we can remove it.
As a consequence, we don't need notify_enter() and notify_leave()
anymore; eliminate them, too.

Give player.c a better name, meaning that the code is used to control
the player thread.

It should be obvious in which thread or context a function is being
executed at runtime.  The code which was left in decode.c is for the
decoder thread itself; give the file a better name.

This is the last of the three variables.  Now we don't need
playerData.h anymore in most sources.

This flag is used internally; it is set by decoder_seek_where(), and
indicates that the decoder plugin has begun the seek process.  It is
used for the case that the decoder plugin has to read data during the
seek process.  Before this patch, that was impossible, because
decoder_read() would refuse to read data unless dc->command is NONE.
This patch is kind of a dirty workaround, and needs to be redesigned
later.

The flag "ready" indicates whether the input stream is ready and it
has parsed all meta data.  Previously, it was impossible for
decodeStart() to see the content type of HTTP input streams, because
at that time, the HTTP response wasn't parsed yet.

Move code which runs in the player thread to player_thread.c.  Having
a lot of player thread code in decode.c isn't easy to understand.

decode.c should be a lot smaller; start by moving all code which
handles cross-fading to crossfade.c.  Also includes camelCase
conversion.

Make the code more readable by hiding big formulas in an inline
function with a nice name.