Fixes accidental suggestions in the beam collision engraver (issue4271054)

[mtsolo]

Reviewers: ,

Message:
Hey all,

A bug just hit the French list.  It seems like a critical regression.

\score {             %avec "surcharge" des ligatures double croches
allongées
   \new Staff {
 \time 2/2
 \set suggestAccidentals = ##t
g'4 fis'8 [  g'8 ]  a'8 [  g'8 a'16 g'16  fis'!16 e'16 ]   |
d'1
    }

}
\score {         %sans "surcharge" des ligatures : bon
       \new Staff {
 \time 2/2
 \set suggestAccidentals = ##t
g'4 fis'8   g'8   a'8   g'8 a'16 g'16  fis'!16 e'16    |
d'1
    }

}

This patch proposes a fix.

Cheers,
Mike

Description:
Fixes accidental suggestions in the beam collision engraver

Please review this at http://codereview.appspot.com/4271054/

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  
39e614c2a15dea10f3b72f88110959c35dc389a1..e0dade7b8ea3bc4d2f9eea3d4437b94102f85c80  
100644
--- a/lily/beam-collision-engraver.cc
+++ b/lily/beam-collision-engraver.cc
@@ -160,7 +160,8 @@ Beam_collision_engraver::acknowledge_note_head  
(Grob_info i)
 void
 Beam_collision_engraver::acknowledge_accidental (Grob_info i)
 {
-  covered_grobs_.push_back (i.grob ());
+  if (!i.grob ()->internal_has_interface (ly_symbol2scm  
("accidental-suggestion-interface")))
+    covered_grobs_.push_back (i.grob ());
 }

 void