add --ast-help

displays a rather cruel description of the AST classes, derived
directly from the node definitions.

lib/ast.js

@@ -43,8 +43,6 @@
 
 "use strict";
 
-var NODE_HIERARCHY = {};
-
 function DEFNODE(type, props, methods, base) {
     if (arguments.length < 4) base = AST_Node;
     if (!props) props = [];
@@ -67,9 +65,11 @@ function DEFNODE(type, props, methods, base) {
         ctor.prototype = proto;
         ctor.BASE = base;
     }
+    if (base) base.SUBCLASSES.push(ctor);
     ctor.prototype.CTOR = ctor;
     ctor.PROPS = props || null;
     ctor.SELF_PROPS = self_props;
+    ctor.SUBCLASSES = [];
     if (type) {
         ctor.prototype.TYPE = ctor.TYPE = type;
     }
@@ -83,10 +83,6 @@ function DEFNODE(type, props, methods, base) {
     ctor.DEFMETHOD = function(name, method) {
         this.prototype[name] = method;
     };
-    NODE_HIERARCHY[type] = {
-        def: ctor,
-        base: base
-    };
     return ctor;
 };