* lily/percent-repeat-engraver.cc (try_music): add measure before

* lily/percent-repeat-engraver.cc (try_music): add measure before
next_moment to future processing moment. Fixes:
percent-repeat-mm-rest.ly
(process_music): don't add moment for 2nd time.

* input/regression/repeat-percent.ly: add mmrests as extra test.

* lily/axis-group-engraver.cc (acknowledge_grob): read
keepAliveInterfaces to decide what to kill.

* ly/engraver-init.ly (AncientRemoveEmptyStaffContext): add
percent-repeat-interface to keepAliveInterfaces. This fixes
percent-repeat-harakiri.