Bad positioning of tuplet numbers on kneed beams with Beam.positions override.

Bad positioning of tuplet numbers on kneed beams with Beam.positions override.

Previously, when Beam.positions was overridden, tuplet numbers on kneed beams
would automatically be placed according to the bracket instead of against
the beam.  This happened because the check for whether the beam was kneed
or not returned false in such cases.  This patch replaces that check.

It also:

--adds a regtest demonstrating behavior with Beam.position overrides
--removes some redundant code