* hesiod/hesiod_p.h (struct hesiod_p): Add classes array.

* hesiod/hesiod_p.h (struct hesiod_p): Add classes array.

	* hesiod/hesiod.c (hesiod_init): Initialize classes.  Fail if no
	valid classes were given or if both are equal.
	(hesiod_resolve): Use ctx->classes instead of hardcoded C_IN
	and C_HS order.
	(parse_config_file): Handle classes keyword.
	* hesiod/README.hesiod: Mention addition of the classes keyword.