Overload the name.

Prepare to migrate away from GLib.  Currently, we're still using GLib
as a backend.

Replaces GLib's GError.

Replace g_strchug() calls with a cheaper implementation.

Use the functions song_save() and song_load() to use the same format
as in the database file for those songs which need the tags.

While this is not useful for the database, it may become useful for
reusing this code for the state file.

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.

Clear the colon.  This simplifies all attribute parsers, because they
can now use strcmp() instead of strncmp().

Fix a minor memory leak.

Changed songvec_load() to song_load().  Added start and end markers
for each song.  Removed the "key" line, it's redundant.

Use a single GString buffer object in all functions loading the
database.  Enlarge it automatically for long lines.  This eliminates
the maximum line length for tag values.  There is still an upper limit
of 512 kB to prevent denial of service, but that's reasonable I guess.

The line buffer had a fixed size of 5 kB, and was allocated on the
stack.  This was too small for some users.  As a hotfix, we're
increasing the buffer size to 32 kB now, allocated on the heap.  In
MPD 0.16, we'll switch to dynamic allocation.

Renamed functions.

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().

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