* lily/context-specced-music-iterator.cc (construct_children):

* lily/context-specced-music-iterator.cc (construct_children):
interpret special context id $uniqueContextId

* lily/context.cc (create_unique_context): new method. Move
creation of unique (\new) contexts into interpreting phase. This
makes

* scm/define-music-properties.scm (all-music-properties): add
quoted-voice-direction

* ly/music-functions-init.ly: killCues function.

* scm/music-functions.scm (cue-substitute): move creation of voice
contexts further to the back.