(handle_dollar, handle_at): Now takes int

(handle_dollar, handle_at): Now takes int
token_type, not braced_code code_kind.  All uses changed.
(SC_PRE_CODE): New state, for scanning after a keyword that
has (or usually has) an immediately-following braced code.
(token_type): New local var, to keep track of which token type
to return when scanning braced code.
(<INITIAL>"%destructor", <INITIAL>"%lex-param",
<INITIAL>"%parse-param", <INITIAL>"%printer,
<INITIAL>"%union"): Set token type and BEGIN SC_PRE_CODE
instead of returning a token type immediately.
(<INITIAL>"{"): Set token type.
(<SC_BRACED_CODE>"}"): Use it.
(handle_action_dollar, handle_action_at): Now returns bool
indicating success.  Fail if ! current_rule; this prevents a core dump.
(handle_symbol_code_dollar, handle_symbol_code_at):
Remove; merge body into caller.
(handle_dollar, handle_at): Complain in invalid contexts.