Parts with differing volta brackets

[Dan Eble]

I request comment on http://lsr.di.unimi.it/LSR/Item?id=872.

The description is "If you have a set of parts to build a score, but they 
differ in the \repeat volta and \alternative layout, it is a good idea to 
display them parallel in one score. . . ."

The fact that the parts are out of sync with each other makes this hard for me 
to read.  I would instead add bracketed alternatives to all parts even if some 
of them have no internal differences.

I found this snippet while looking for a use case for moving the 
Repeat_acknowledge_engraver.  If anyone has a more compelling case, I would 
like to hear it.  I don't see a regression test that covers it, which is risky 
if it's something we expect to support.

Thanks,
— 
Dan