Add a variable to pass in the nested user.

dist/openpam/include/security/pam_constants.h

@@ -126,6 +126,7 @@ enum {
 	PAM_AUTHTOK_PROMPT		=  11,		/* OpenPAM extension */
 	PAM_OLDAUTHTOK_PROMPT		=  12,		/* OpenPAM extension */
 	PAM_SOCKADDR			=  13,		/* NetBSD extension */
+	PAM_NUSER			=  14,		/* NetBSD extension */
 	PAM_NUM_ITEMS					/* OpenPAM extension */
 };