ENH: code simplification, improvements for reading dictionary variables

- Now accept '/' when reading variables without requiring
  a surrounding '{}'

- fix some degenerate parsing cases when the first character is
  already bad.

  Eg, $"abc" would have previously parsed as a <$"> variable, even
  although a double quote is not a valid variable character.

  Now emits a warning and parses as a '$' token and a string token.

src/OpenFOAM/primitives/strings/stringOps/stringOps.C

@@ -277,7 +277,9 @@ namespace
 //
 // Similar to word::valid(), except we don't have the benefit of a parser
 // to filter out other unacceptable entries for us.
-
+//
+// Does not currently accept '/' in a variable name.
+// We would like "$file/$name" to expand as two variables.
 static inline bool validVariableChar(char c)
 {
     return