Re: Auto_change_iterator: move some state from C++ to Scheme (issue 248470043 by address@hidden)

[nine . fierce . ballads]

I haven't yet reached an understanding of what should be done about
make-non-relative-music.  Some testing would help me understand more
deeply why it is good for partcombine and whether it would be good for
autochange, but I have been short on time.  It's on my to-do list, but I
do not want to delay this patch for it.

https://codereview.appspot.com/248470043/