+ preserve changes to \transpose in an hboxed tremolo command
+ test that musixtex.tex has already been loaded in some extensions:
+ musixps, musixec, musixhv, musixplt, musixtmr, musixppff
+ changed from \it to \ppff in several places
+ support new command \setinterstaff{n}{m}
+ define \largenotesize, \Largenotesize
+ corrected typos \twtybf[g] \svtbf[g]
