clusters interrupted by rests but not multi-measure rests
\makeClusters \music produces expected output when \music contains a
rest, but multi-measure rests and skips do not interrupt the cluster.
Whilst the documentation for Clusters includes under Known issues and
warnings: "Separate clusters need a separating rest between them",
there doesn't seem to be an issue for this in the tracker. Surely this
is not the intended behaviour?