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/defaults.c

@@ -591,6 +591,7 @@ init_defaults(void)
     def_log_denied = true;
     def_log_format = sudo;
     def_runas_allow_unknown_id = false;
+    def_noninteractive_auth = false;
 
     /* Syslog options need special care since they both strings and ints */
 #if (LOGGING & SLOG_SYSLOG)