Beam collision scoring (issue4174043)

[k-ohara5a5a]

I tried this patch on half a dozen piano and orchestral scores and saw
no bad side-effects.

Only manual [] beams are checked for collisions. I cannot remember why
this is so, and could not find the reason in the email archive.  The
collision avoidance looks good for all beams, if possible.

I checked that manual beams do indeed avoid the things on the list in
the previous commit for beam_collision_engraver :
(note_head); (accidental); (clef); (key_signature);(time_signature);
(bar_line); (beam);

Bar lines should probably not be counted for collisions.  Certainly
intersecting a bar line is less of a demerit than crossing a stem.  The
only reference I have at hand (Kurt Stone) says nothing to this
question, unfortunately.

In any event, the current patch allows beams to intesect the cross-staff
portion of a bar line, so my piano example
(http://www.mutopiaproject.org/cgibin/piece-info.cgi?id=1779) came out
just fine.


http://codereview.appspot.com/4174043/diff/2001/input/regression/beam-collision-prefatory-matter.ly
File input/regression/beam-collision-prefatory-matter.ly (right):

http://codereview.appspot.com/4174043/diff/2001/input/regression/beam-collision-prefatory-matter.ly#newcode25
input/regression/beam-collision-prefatory-matter.ly:25: \key f \major
suggest \bar "||" before \key, so the humans checking regtests recognize
these as key changes.

http://codereview.appspot.com/4174043/