Improve -v2 diagnostic message for typedef

alias is not a 1-to-1 replacement for typedef and in many cases
struct based workaround is absolutely necessry.

src/parse.c

@@ -2185,7 +2185,7 @@ Dsymbols *Parser::parseDeclarations()
         case TOKtypedef:
             if (global.params.Dversion >= 3 && mod && mod->isRoot())
             {
-                warning(loc, "use alias for D2 rather than typedef");
+                warning(loc, "typedef is deprecated in D2, use either alias or custom struct wrapper");
             }
         case TOKalias:
             tok = token.value;