Make arguments like Context.GrobName accessible as symbol lists

input/regression/spanner-break-overshoot.ly

-\version "2.17.5"
+\version "2.17.6"
 
 \header {
   texidoc = "The @code{break-overshoot} property sets the amount that
 a spanner (in this case: the beam and tuplet bracket) in case of a line
 break extends beyond the rightmost column and extends to the left beyond the
 prefatory matter."
 }
 
 \paper { ragged-right = ##t }
 
 \relative c'' {
-  \override Beam break-overshoot = #'(1.0 . 2.0)
-  \override TupletBracket break-overshoot = #'(1.0 . 2.0)
-  \override TupletBracket bracket-visibility = ##t
-  \override Beam breakable = ##t
+  \override Beam.break-overshoot = #'(1.0 . 2.0)
+  \override TupletBracket.break-overshoot = #'(1.0 . 2.0)
+  \override TupletBracket.bracket-visibility = ##t
+  \override Beam.breakable = ##t
   c2.. \times 2/3 { c8.[ \break c8.] }
 }