Fixes regression from commit e96779de.

Leave that to the caller, allowing it to modify multiple items at a
time.

The check for unsigned underflow is fragile and unreliable.

Make sure the queue "owns" all song objects, so nobody else can free
them.

Sorts remaining songs by priority.  This can be used for the
much-demanded "queue feature".

Check consume mode in queue_next_order(), because the current song
would be deleted as soon as it's finished; it cannot be played again.

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.

Renamed idToPosition.

Consume mode removes each song played

When single mode is enabled, after current song it stops playback,
or it replay same song if repeat mode is activated.

The smartstop feature is a way to tell mpd to stop playing after
current song.
This patche provides:
- 'state' command returns 'smartstop' state (1 or 0)
- 'smartstop' can activate or not the smartstop state
- when song is terminated, mpd stops playing and smartstop is set to 0

The move command now accepts a range for the first argument, in the same
form as other range commands, e.g. move 15:17 3.  The first song in the
range is placed at the destination position. Note that as with other
range commands, the range is inclusive on the left only; this example
would move only songs 15 and 16, not 17.

[mk: fixed signed/unsigned warnings; use G_MAXUINT instead of
UINT_MAX]

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.

Commit f78cddb4 introduced a regression: after a song was moved, the
order array was not updated (in random mode).  This caused MPD to
think the "current" song has changed when you moved something to the
position of the current song.

This function shuffles the last song of a range.  This is used by
addSongToPlaylist().

This patch fixes a regression introduced by commit aa9ffc.

The function shuffles the virtual order of songs, but does not move
them physically.  This is used in random mode.

The new function replaces playlist.c's randomizeOrder() function,
which was aware of playlist.current and playlist.queued.  The latter
is always -1 anyway, and the former as preserved by the caller, by
converting playlist.current to a position, and then back to an order
number.