* lily/beam-quanting.cc (score_forbidden_quants): make forbidden

* 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.

* lily/new-slur.cc: cleanup, split in functions.

* lily/new-slur.cc (score_encompass): variable head-distance penalty.

* lily/new-slur.cc (print): use debug-slur-quanting paper var.