* lily/include/global-context.hh (Context): clean-up data hiding.

* lily/include/global-context.hh (Context): clean-up data hiding.

* lily/include/music-iterator.hh (class Music_iterator): clean-up
data hiding.

* lily/include/grace-fixup.hh (struct Grace_fixup): new file.

* input/regression/stem-shorten.ly: add chord case.

* lily/stem.cc (get_default_stem_end_position): shorten stems
triggered by note-head positions, not by forced-direction. This
fixes a bug with too short stems.