Add sudoers option to perform authentication even in non-interative mode.

If noninteractive_auth is set, authentication methods that do not
require input from the user's terminal may proceed.  It is off by
default, which restores the pre-1.9.9 behavior of "sudo -n".

plugins/sudoers/def_data.c

@@ -645,6 +645,10 @@ struct sudo_defs_types sudo_defs_table[] = {
 	"rlimit_stack", T_RLIMIT|T_BOOL,
 	N_("The maximum size to which the process's stack may grow (in bytes): %s"),
 	NULL,
+    }, {
+	"noninteractive_auth", T_FLAG,
+	N_("Attempt authentication even when in non-interactive mode"),
+	NULL,
     }, {
 	"log_passwords", T_FLAG,
 	N_("Store plaintext passwords in I/O log input"),