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.

[mk: fixed whitespace errors; use delete_song() instead of
songvec_delete()]

The GLIB_CHECK_VERSION() macro was used improperly, which broke build
on GLib < 2.14.  Add a "!" for negation.

The lastfm input plugin enables MPD to play lastfm:// URLs.  This
plugin is not complete yet: it plays only the first song in the
last.fm playlist, and the playlist parser isn't even implemented
properly.

Allow input plugins to configure with an "input" block in mpd.conf.
Also allow the user to disable a plugin completely.

Instead of hard-coding the plugin global initialization in
input_stream_global_init(), make it walk the plugin list and
initialize all plugins.

Create a sub directory for input plugins.