*added a b_stopped flag to interface playlist to have a stop function in
interface plugins. As a consequence, the playlist no longer loops on end
but wait for the user to press 'play' or to add another item (gtk/gnome
interface). I think that other plugins are broken but it shouldn't be
difficult to repair: just add a 'p_main->p_playlist->b_stopped = 0' in
play functions and 'p_main->p_playlist->b_stopped = 1' when you have to
stop.

*Updated gtk interface so that it has the same features as gnome. I
think I will merge the code so that we don't have to copy and paste each
change. Only the .glade file would be different.