* lily/beam-quanting.cc (score_forbidden_quants): make forbidden
quant penalty dependent on how much the line is in the gap.
* input/regression/grace-stem-length.ly: new file.
* lily/beam-quanting.cc (score_forbidden_quants): remove
interquant check. The penalty of 1000 is much too harsh, and the
inter case should be caught by check-staff-line-in-gap check.