Markup error: braces not properly marked in dictionary display

grammer productions.
Fixes SF bug #520959.

Doc/ref/ref5.tex

@@ -211,7 +211,7 @@ enclosed in curly braces:
 
 \begin{productionlist}
   \production{dict_display}
-             {"{" [\token{key_datum_list}] "}"}
+             {"\{" [\token{key_datum_list}] "\}"}
   \production{key_datum_list}
              {\token{key_datum} ("," \token{key_datum})* [","]}
   \production{key_datum}