Always assert that the audio format of the new chunk is valid.

Hello,

While compiling latest git I've received a compile error in the
httpd_output_plugin.
Small patch attached.

Patrik

The string comparison should be "!= 0", not "== 0".  Ouch.

The player thread must reset pc.next_song after seeking, even if that
operation has failed.  This patch adds an assertion.

The only pc_seek() caller clears the error, rendering the check
useless.  Even if the previous PLAY command resulted in a player
error, this check is not very useful.

Renamed playerSeek() to pc_seek() to get rid of CamelCase.  Convert
the return value to bool.

If the UFID frame's owner is "http://musicbrainz.org", assume its
value is the MusicBrainz track id.

Flush the encoder before calling encoder_tag().  The first page
generated by the encoder after sending the tag will be the new
"header" page, which is sent to all HTTP clients when they connect.
This is a little bit specific to the vorbis encoder, but there are no
other encoders which support tags (yet).

Moved some code from httpd_output_encode_and_play() into separate
functions httpd_output_broadcast_page() and
httpd_output_encoder_to_clients().

There's no reason to send both encoder tags and Icy-Metadata to the
client.  Let's disable Icy-Metadata when the encoder supports embedded
tags.

When a new tag is set, end the current stream and begin a new one.
Use vorbis_analysis_headerout() to write a full ogg header.  This
fixes a problem with icecast: after a song change in MPD, icecast
stops forwarding ogg packets to its clients.

In the tag() method, MPD guarantees that it does not pass tag==NULL.
Converted the runtime check to an assertion.

The second parameter of zzip_dir_open() is a pointer.  Pass the NULL
pointer instead of 0 (with implicit conversion at compile time).

Don't loop over source files, do all checks in one run.

Remove mpd.spec and makerpm.sh. It was never used or maintained
and the distributors take care of this kinda thing now anyhow.

Added the per-device option "mixer_enabled" which allows users to
disable the hardware mixer of an audio output.

sticker_delete_value() deletes only one value in a sticker, while
the old function sticker_delete() deletes all values.

When a song was in the database twice (which shouldn't happen), and
the first song had no tag items, MPD calledd tag_free(NULL).  Add a
check to that source location, and an assertion to tag_free().

strncasecmp() is locale dependent, making it a bad choice for internal
string comparisons.

strcasecmp() is locale dependent, making it a bad choice for internal
string comparisons.

strcasecmp() is locale dependent, making it a bad choice for internal
string comparisons.

strcasecmp() is locale dependent, making it a bad choice for internal
string comparisons.

strcasecmp() is locale dependent, making it a bad choice for internal
string comparisons.

strcasecmp() is locale dependent, making it a bad choice for internal
string comparisons.

strcasecmp() is locale dependent, making it a bad choice for internal
string comparisons.

strcasecmp() is locale dependent, making it a bad choice for internal
string comparisons.

strcasecmp() is locale dependent, making it a bad choice for internal
string comparisons.

strcasecmp() is locale dependent, making it a bad choice for internal
string comparisons.

This allows you to select controls with duplicate names.