Fix Tracker 918, Add extra RemoveEmpty*StaffContext functions to support "Frenched" scores (issue180095)

[ian]

Reviewers: ,

Message:
New patch-set uploaded with regressions in engraver-init.ly fixed.

Now OK to push?

Cheers,
Ian

Description:
Fix Tracker 918, Add extra RemoveEmpty*StaffContext functions to support
"Frenched" scores
with DrumStaff, TabStaff and RhythmicStaff staves.

Add new definitions in ly/engraver-int.ly and new regression tests.

Fix Tracker 918, Add extra RemoveEmpty*StaffContext functions to support
"Frenched" scores with DrumStaff, TabStaff and RhythmicStaff staves.

Add new definitions in ly/engraver-int.ly and new regression tests.

Please review this at http://codereview.appspot.com/180095

Affected files:
  A input/regression/hara-kiri-drumstaff.ly
  M input/regression/hara-kiri-percent-repeat.ly
  A input/regression/hara-kiri-rhythmicstaff.ly
  A input/regression/hara-kiri-tabstaff.ly
  M ly/engraver-init.ly