lily/include/context-def.hh: rename from translator-def.hh

lily/include/context-def.hh: rename from translator-def.hh

lily/stem.cc (calc_stem_info): use
Staff_symbol_referencer::staff_space

lily/beam-quanting.cc (quanting): scale Stem_info

lily/beam.cc (rest_collision_callback): use minimum-distance
property for rest/beam collisions.
(rest_collision_callback): bugfixes.

lily/system.cc (post_processing): extra-offset is now relative
to the size of the current staff.

scm/music-functions.scm (notice-the-events-for-pc): record all
voices, only analyze "one" and "two".

lily/recording-group-engraver.cc (finalize): bugfix: want self,
not parent.