Re: Sketchy sketch for a modification to the typesetting backend. (issue4446060)

[mtsolo]

I realized that it was way too restrictive to have cross-staff beams
avoid stems and beams - Reinhold had sent out a Beethoven example a
while back that would need cross staff beams to take other beams into
consideration.

The real problem is that certain cross staff beams are not in fact cross
staff beams.  This patch weeds them out of beam collision work via a new
function Beam::is_fake_cross_staff.  Ultimately, this sorta logic can
disappear once the beam collision engraver moves up to the score level,
which seems like something that'll cause several bugs in the unstable
version (if history is any indication) and thus is something I'm holding
off on until this current crop of bugs dies down.

http://codereview.appspot.com/4446060/