* Documentation/user/instrument-notation.itely: Cleanup: Remove

	* Documentation/user/instrument-notation.itely: Cleanup: Remove
	annoying skip notes from mensural ligature example.  Update
	@refbugs for ligatures and mensural ligatures.

	* lily/coherent-ligature-engraver.cc,
	lily/include/coherent-ligature-engraver.hh,
	lily/mensural-ligature-engraver.cc,
	lily/vaticana-ligature-engraver.cc: Revise code for item
	reparentizing.  There should now be less programming_error
	messages.

	* lily/mensural-ligature-engraver.cc: Improve placement of dots.

	* lily/mensural-ligature.cc, lily/vaticana-ligature.cc:
	Maintenance bugfix: Don't create empty Stencil (), but empty box
	instead.  This fix should eliminate some programming_error
	messages.

	* ly/engraver-init.ly (MensuralStaff): Set default accidental
	style.

	* input/regression/mensural-ligatures.ly: Maintenance bugfix: Move
	\layout block _before_ score.