* lily/include/context.hh (class Context): make members protected.

* lily/include/context.hh (class Context): make members protected.
(children_contexts): new accessor function.

* lily/include/context.hh (class Context): make daddy_context_
private.

* lily/lyric-engraver.cc (get_voice_to_lyrics): recursively go
higher for finding Voice. (backportme)

* lily/include/context.hh (class Context): remove
find_context_below() as a method.