* lib/prototypes.h, src/suauth.c, src/su.c (check_su_auth): Do not

	* lib/prototypes.h, src/suauth.c, src/su.c (check_su_auth): Do not
	use the pwent global variable to communicate between APIs of
	different files. Added boolean parameter su_to_root to
	check_su_auth().
	* src/su.c (check_perms): Return the passwd entry of the finally
	authenticated user. Remove usage of the pwent variable.
	* src/su.c: The password of the caller is the one from the
	spwd structure only if the passwd's password is 'x'.