bench.pl: Pass directives as a list instead of as a string.

	* etc/bench.pl.in (&directives): New.
	(&triangular_grammar, &calc_grammar): Use it to format the Bison
	directives.
	(&triangular_grammar): Do use the directives (were ignored).
	(&bench_grammar, &bench_push_parser): Adjust to pass lists of
	directives.