(LilyPond-lilypond-command): command used to compile LY files (useful

for adding eg. "-I" args)
(LilyPond-command-alist): use `LilyPond-lilypond-command'. Add a
2Gnome command for gnome backend.
(LilyPond-command-formatgnome): call the 2Gnome command. key binding:
C-c C-g