* lily/vaticana-ligature-engraver.cc, lily/gregorian-ligature.cc,
lily/include/gregorian-ligature.hh: print warning when ignoring
head prefixes on flexa shapes
* lily/vaticana-ligature-engraver.cc: bugfix: always add an extra
space before a series of inclinatum heads
* lily/vaticana-ligature-engraver.cc, lily/gregorian-ligature.cc,
lily/include/gregorian-ligature.hh: junked AFTER_VIRGA; small
cleanups
* mf/parmesan-custodes.mf: redesigned custos; fixed stem length
and char_box