If not root and not setuid, print warning.

git-svn-id: svn://svn.h5l.se/heimdal/trunk/heimdal@21179 ec53bebd-3082-4978-b11e-865c3cabbd6b

appl/su/su.c

@@ -440,6 +440,9 @@ main(int argc, char **argv)
     else
 	su_user = argv[optind++];
 
+    if (!issuid() && getuid() != 0)
+	warnx("Not setuid and you are root, expect this to fail");
+
     pwd = k_getpwnam(su_user);
     if(pwd == NULL)
 	errx (1, "unknown login %s", su_user);