%param.

%param.

Provide a means to factor lex-param and parse-param common
declarations.

	* src/parse-gram.y (param_type): New.
	Define a %printer for it.
	(add_param): Use it.
	(%parse-param, %lex-param): Merge into...
	(%parse): this new token.
	Adjust the grammar to use it.
	* src/scan-gram.l (RETURN_VALUE): New.
	(RETURN_PERCENT_FLAG): Use it.
	(RETURN_PERCENT_PARAM): New.
	Use it to support %parse-param, %lex-param and %param.