Make arguments like Context.GrobName accessible as symbol lists

input/regression/breathing-sign.ly

-\version "2.16.0"
+\version "2.17.6"
 \header{
   texidoc="
 Breathing signs are available in different tastes: commas (default),
 ticks, vees and `railroad tracks' (caesura)."
 }
 
 
 {
   %% Modern notation:
   \new Staff {
     \relative c'' {
       %% by default, \breathe uses the rcomma, just as if saying:
-      %% \override BreathingSign #'text =
+      %% \override BreathingSign.text =
       %%   #(make-musicglyph-markup "scripts.rcomma")
       %%
       c4 c \breathe c c |
 
       %% rvarcomma and lvarcomma are variations of the default rcomma
       %% and lcomma
       %%
-      \override Staff.BreathingSign #'text =
+      \override Staff.BreathingSign.text =
         #(make-musicglyph-markup "scripts.rvarcomma")
       c4 c \breathe c c |
 
       %% wedge
       %%
-      \override BreathingSign #'text =
+      \override BreathingSign.text =
         #(make-musicglyph-markup "scripts.upbow")
       c4 c \breathe c c |
 
       %% caesurae
       %%
-      \override BreathingSign #'text =
+      \override BreathingSign.text =
         #(make-musicglyph-markup "scripts.caesura.curved")
       c4 c \breathe c c |
 
-      \override BreathingSign #'text =
+      \override BreathingSign.text =
         #(make-musicglyph-markup "scripts.caesura.straight")
       c4 c \breathe c c |
     }
   }
 }