Tweaks regtest and adds avoid-collisions property (issue4022045)

[percival . music . ca]

LGTM.


http://codereview.appspot.com/4022045/diff/12001/input/regression/beam-collision.ly
File input/regression/beam-collision.ly (right):

http://codereview.appspot.com/4022045/diff/12001/input/regression/beam-collision.ly#newcode15
input/regression/beam-collision.ly:15: \clef bass g,,,8[ \clef treble
d''8]
Could the notes go on their own line?

If there's no other problems with this draft, then don't bother --
there's no point being really fussy with .ly syntax in the regtests --
but I expect there's still a few more drafts to come, and it would be
easier to read if notes were a little bit more separate from clefs,
overrides, and the like.

http://codereview.appspot.com/4022045/diff/12001/input/regression/beam-collision.ly#newcode26
input/regression/beam-collision.ly:26: \once \override Voice . Beam
#'avoid-collisions = ##f c8[ c c c] }
Could the notes go on the next line, leaving the override by itself on
the line?

Also, could I get a
^"turn off collision avoidance"
so that it's obvious in the image that these collisions are ok?  :)

http://codereview.appspot.com/4022045/diff/12001/input/regression/beam-collision.ly#newcode54
input/regression/beam-collision.ly:54: s8 f s g s a s b s c s d s e  }
I see a stem collision for the d and e.  I'm not complaining about this,
but consider adding a
  ^"no solution possible; stem collides with notehead"
if this is intentional/acceptable.

Basically, imagine that you're a poor bug squad member doing our
infrequent full regtest check.  You know nothing about programming, and
you have 900+ regtests to review, so you're trying to go through each
regtest in 30 seconds or so.  Anything you can do to make the .png more
clear is a good thing.  :)

http://codereview.appspot.com/4022045/