* lily/beam.cc (set_stem_lengths): single-stem-beam fix.

* lily/beam.cc (set_stem_lengths): single-stem-beam fix.

* stepmake/stepmake/c-rules.make ($(outdir)/%.c): use -o for flex.

* lily/beam-quanting.cc (quanting): check french-beaming per stem.
(score_stem_lengths): do something sensible for single stem beams.

* lily/beam.cc (least_squares): add kludge for single stem beams.

* scripts/convert-ly.py (FatalConversionError.sub_alteration): add
keySignature to list of broken things.

* input/regression/keys.ly: fix.