Make arguments like Context.GrobName accessible as symbol lists

Documentation/snippets/new/ancient-notation-template----modern-transcription-of-gregorian-music.ly

-\version "2.16.0"
+\version "2.17.6"
 
 \header {
   lsrtags = "vocal-music, ancient-notation, template"
 
   texidoc = "
 This example demonstrates how to do modern transcription of Gregorian
 music. Gregorian music has no measure, no stems; it uses only half and
 quarter note heads, and special marks, indicating rests of different
 length.
 
@@ skipping 17 matching lines @@
 \score {
   \new Staff <<
     \new Voice = "melody" \chant
     \new Lyrics = "one" \lyricsto melody \verba
   >>
   \layout {
     \context {
       \Staff
       \remove "Time_signature_engraver"
       \remove "Bar_engraver"
-      \override Stem #'transparent = ##t
-      \override Flag #'transparent = ##t
+      \override Stem.transparent = ##t
+      \override Flag.transparent = ##t
     }
     \context {
       \Voice
-      \override Stem #'length = #0
+      \override Stem.length = #0
     }
     \context {
       \Score
       barAlways = ##t
     }
   }
 }