* lily/rest.cc (polyphonic_offset_callback): new function. Do

* lily/rest.cc (polyphonic_offset_callback): new function. Do
vertical positioning for polyphony, without RestCollision object.

* lily/note-column.cc (add_head): prevent rests & note heads on
one stem.

* lily/rest-collision.cc (do_shift): ignore rests with beams.
(do_shift): rewrite only-rests case: use common refpoints: the
routine will have sensible results when other rest-translations
have taken place.

* lily/simple-spacer.cc (solve): cleanup: remove code for linelen
< 0 case.

* input/GNUmakefile (SUBDIRS): remove ascii-art