This function checks whether a prerequisite for a feature was found.

When MPD_AUTO_DISABLED prints a fatal error message, include the
feature name.  This might be an important piece of information for the
user, just in case the preceding line doesn't tell him.

Fail if the iso9660 plugin is enabled but not found.

Fail if the zzip plugin is enabled but not found.

icy_server_metadata_string() is only called by
icy_server_metadata_page().

Plain "bool" consumes only one byte instead of four.

In HTTP, header names are case insensitive.

[mk: folded with patch "Put icy related functions in extra source
files"; moved icy_server.c from HAVE_CURL to ENABLE_HTTPD_OUTPUT;
removed an unused variable]

When a new song starts playing, send its tag (song->tag) to the music
pipe.  This allows output plugins to render tags for all songs, not
only those with embedded tags understood by the decoder plugin.

Most of that was already implemented, and for other feature requests,
we have the bug tracker.

A <varlistentry> was accidentally added before the
beginning of the intended <variablelist>

The "lastfm" input plugin is far from complete, because MPD does not
support nesting playlists yet.  The "fluidsynth" decoder plugin
suffers from shortcomings in the libfluidsynth library:

 http://www.mail-archive.com/fluid-dev@nongnu.org/msg01099.html

The httpd_client_check_queue() callback function does not use its
"user_data" argument.  Don't pass any, and fix the gcc warning.

Don't append those two CFLAGS/LIBS in configure.ac.

Renamed --enable-oggvorbis-encoder to --enable-vorbis-encoder.

Use MPD_AUTO_RESULT(), and set enable_lame to "auto" by default.

Don't append LAME_CFLAGS/LAME_LIBS to MPD_CFLAGS/MPD_LIBS in
configure.ac.  Export them via AC_SUBST() instead.

Use MPD_AUTO_PKG().  Removed the checks for the Ogg Vorbis decoder
plugin, this is not directly related.

Use the new $need_encoder variable to determine whether encoder
plugins would actually be used if they were available.

Enable the HTTPD output plugin by default, provided that the encoder
API is available.

This patch makes the shout checks use MPD_AUTO_PKG() instead of
manually invoking PKG_CHECK_MODULES().  It sets the default value to
"auto" instead of "no".

$enable_encoder specifies whether one or more encoder plugins are
enabled.  This simplifies several checks, and allows easier
integration of more encoder plugins.