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.

Move everything which belongs together into one common struct.  This
simplifies the implementation of several queue operations.

Attempt to untie the playlist.c knot: moved the playlist storage code
to queue.c, struct queue.