Turns off beam collision for cross-staff beams (issue4423062)

[mtsolo]

Reviewers: ,

Description:
Turns off beam collision for cross-staff beams

Please review this at http://codereview.appspot.com/4423062/

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  
8880e9c6e34bf68c306fe9d47005fac3e280a3fd..d705a1e736175df45dfd17ec87c90b12af1d1a56  
100644
--- a/lily/beam-collision-engraver.cc
+++ b/lily/beam-collision-engraver.cc
@@ -76,6 +76,9 @@ Beam_collision_engraver::finalize ()
   for (vsize i = 0; i < beams_.size (); i++)
     {
       Grob *beam_grob = beams_[i].grob ();
+      if (Beam::is_cross_staff (beam_grob))
+        continue;
+
       Context *beam_context = beams_[i].context ();

       Interval_t<int> beam_spanned_rank_ =  
beam_grob->spanned_rank_interval ();