Backporting for 2.14.2

[Carl Sorensen]

I'm trying to get ready for release 2.14.2.  In general, I'd like bugfixes
from 2.15.x to show up in 2.14.2.

To do this, I'm searching the issues, looking for fixed_2_15_1,
fixed_2_15_2, fixed_2_15_3.  If I can backport, I do so, then mark the issue
fixed_2_14_2.  This system seems to work pretty well.

I have a question about issue 1655.  In order to allow longa rests in
MultiMeasureRest grobs, a couple of new properties are added:
round-to-longer-rest and usable-duration-logs.  Additionally, one property
is deleted: use-breve-rest.  In essence, use-breve-rest is substituted with
usable-duration-logs.

Am I right in assuming that this syntax change prevents backporting this fix
to 2.14.x?  IIUC, we want the stable version to have stable syntax.

Thanks,

Carl