* lily/beam.cc (set_minimum_dy): new function. Round non-zero

* lily/beam.cc (set_minimum_dy): new function. Round non-zero
small slope up to smallest quant. This prevents small slopes from
getting rounded to zero.

* lily/beam-quanting.cc (quanting): don't allow dy_mus slopes that
are smaller than the smallest quant.

* scm/define-grobs.scm (all-grob-descriptions): fix order of
key-cancellation.

This fixes: morgenlied.ly and input/regression/beam-concave.ly