Make arguments like Context.GrobName accessible as symbol lists

input/regression/breve-extent.ly

Index: input/regression/breve-extent.ly
diff --git a/input/regression/breve-extent.ly b/input/regression/breve-extent.ly
index 257445615db087a75cb91645c6b9cf8f3e36cba0..f55588e5245edec061c86a4733bc5374ea108e0b 100644
--- a/input/regression/breve-extent.ly
+++ b/input/regression/breve-extent.ly
@@ -1,4 +1,4 @@
-\version "2.16.0"
+\version "2.17.6"
 
 \header  {
   texidoc = "LilyPond knows that breves and longas are wider than whole notes
@@ -11,21 +11,20 @@
   gis'1
   gis'\breve*1/2
   gis'\longa*1/4
-  \override NoteHead #'style = #'altdefault 
+  \override NoteHead.style = #'altdefault 
   gis'\breve*1/2
 }
 
 \score {
     \new Staff {
       \repeat unfold 8 { a'\breve*1/16 }
-      \override NoteHead #'style = #'altdefault 
+      \override NoteHead.style = #'altdefault 
       \repeat unfold 8 { a'\breve*1/16 }
     }
     \layout {
         \context {
             \Score
-            \override SpacingSpanner
-            #'common-shortest-duration = #(ly:make-moment 1 1 )
+            \override SpacingSpanner.common-shortest-duration = #(ly:make-moment 1 1 )
         }
     }
 }