* guardians.c (F_GREEDY, F_LISTED, F_DESTROYED, GREEDY_P,

	* guardians.c (F_GREEDY, F_LISTED, F_DESTROYED, GREEDY_P,
 	SET_GREEDY, LISTED_P, SET_LISTED, CLR_LISTED, DESTROYED_P,
 	SET_DESTROYED): new defines/macros.
	(GUARDIAN_LIVE, GUARDIAN_ZOMBIES, GUARDIAN_NEXT): deleted.
	(add_to_live_list): takes a `guardian_t *' now, not SCM.
	(guardian_print): print more info.
	(guardian_apply): check if the guardian is destroyed, and throw an
 	error if so.  take one more optional argument `throw_p'.
	(scm_guard): depending on the value of `throw_p', return a boolean
 	result.
	(scm_get_one_zombie): remove redundant property test.
	(guardian_t): represent the various (currently 3, I hope nothing
 	more gets added) boolean fields as bit flags.
	(scm_guardian_destroyed_p, scm_guardian_greedy_p): new predicates.
	(scm_destroy_guardian_x): new procedure.

	* guardians.h: added prototypes for `scm_guardian_greedy_p' and
	`scm_guardian_destroyed_p'.  changed prototype for `scm_guard'.