Trivial 15-line bison excercise: Implemented expressions including

user-defined numeric symbols. Whenever possible, use `expr' instead
of `NUM' to get full express ion power :-)

nest/config.Y

@@ -54,9 +54,10 @@ proto_name:
 
 proto_item:
    /* EMPTY */
- | PREFERENCE NUM {
+ | PREFERENCE expr {
      if ($2 < 0 || $2 > 255) cf_error("Invalid preference");
      this_proto->preference = $2;
+die("pref=%d", $2);
    }
  ;