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.

Convert a string into a tag_type enum.

Like tag_merge(), but can deal with NULL parameters, and frees both
tag objects.

This function has always been broken, but fortunately nobody used it.

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.

Convert a string into a tag_type enum.

The tag_id3.c library supports both the documented "TSO2" tag, and the
inofficial TXXX/ALBUMARTISTSORT.

The Vorbis/FLAC decoder automatically supports the new tag, without
further change.

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().

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

Use GLib the logging functions g_debug(), g_error() instead.

This updates the copyright header to all be the same, which is
pretty much an update of where to mail request for a copy of the GPL
and the years of the MPD project. This also puts all committers under
'The Music Player Project' umbrella. These entries should go
individually in the AUTHORS file, for consistancy.

Renamed functions and variables.

Overwrite invalid UTF-8 sequences with question marks.

There's no point in declaring num_items as a uint8_t, it doesn't save
any space, due to padding.  This allows us to lift the articial "255
items" limitation.

Renamed numOfItems to num_items.

This variable doesn't have a role since 80799fa8.

On some platforms, g_free() must be used for memory allocated by
GLib.  This patch intends to correct a lot of occurrences, but is
probably not complete.

All config_get_block_*() functions should accept constant config_param
pointers.

config_get_string() is easier to use than config_get_param() because
it unpacks the config_param struct.

Added all important id tags from the MusicBrainz wiki:

 http://musicbrainz.org/doc/MusicBrainzTag

This should automatically enable its suport in the vorbis and flac
decoder plugins.

Renamed functions, types, variables.

Added TAG_ITEM_ALBUM_ARTIST.

With this patch, MPD should be able to read the (inofficial)
"ALBUMARTIST" Vorbis comment.  Implementations in other decoder
plugins will follow soon.

Use g_strndup() instead of g_memdup().

Pass NULL instead of &error to g_convert().  We're not interested in
the error object.

tag_merges() merges the data from two tag objects into one.

Don't use g_strescape(), because it escapes all non-ASCII characters.
Add a new function which clears all non-printable characters, not just
"newline".

This always allocates strings on the heap, but we can delete the
stripReturnChar() function now.

tag_has_type() checks whether the tag contains one or more items with
the specified type.

Don't use the deprecated functions from utils.h.

Eliminate code already provided by GLib.