Removes cross-staff beams from the collision grob array (issue4432063)

[mtsolo]

Reviewers: ,

Message:
This may be killing a fly with a sledgehammer.

Another alternative may be to create an internal property for beams
called "automatic" that is set to true if a beam is an autobeam and then
apply the fix in this patch only to beams that are cross staff _and_
automatically created (in issue 1632, the problem goes away if you use
manual beams).

Description:
Removes cross-staff beams from the collision grob array

Please review this at http://codereview.appspot.com/4432063/

Affected files:
  M lily/beam-collision-engraver.cc


Index: lily/beam-collision-engraver.cc
diff --git a/lily/beam-collision-engraver.cc  
b/lily/beam-collision-engraver.cc
index  
19e9b82caf2c1d482d1a944a5da588ed89298c0b..e918793b6beb0303955c6ab5ae75db71ae6d2737  
100644
--- a/lily/beam-collision-engraver.cc
+++ b/lily/beam-collision-engraver.cc
@@ -105,7 +105,8 @@ Beam_collision_engraver::finalize ()
               && !(to_boolean (beam_grob->get_property  
("collision-voice-only"))
                    && (covered_grob_context != beam_context))
               && !(Beam::has_interface (covered_grob)
-                   && (covered_grob_spanned_rank[LEFT] <=  
beam_spanned_rank_[LEFT]))
+                   && ((covered_grob_spanned_rank[LEFT] <=  
beam_spanned_rank_[LEFT])
+                       || Beam::is_cross_staff (covered_grob)))
               && covered_grob_has_interface (covered_grob, beam_grob))
             {
               // Do not consider note heads attached to the beam.