Explicitly track "script.subr" which wasn't showing up in the graph because

it's not used by anything within bsdconfig nor any modules (rather, the
script.subr include is designed to be used externally -- nonetheless we
want to track it in the modular graph outputs showing includes).

usr.sbin/bsdconfig/dot/dot

@@ -298,6 +298,12 @@ if [ "$SHOW_INCLUDES" ]; then
 	done
 fi
 
+#
+# Add script.subr to includes if it exists
+#
+[ -f $BSDCFG_SHARE/script.subr ] &&
+	include_file_list="$include_file_list script.subr"
+
 #
 # Start the directional-graph (digraph) output
 #