added $propdoc to AST nodes and some cleanups

hopefully we can make the AST documentation self-generating

lib/transform.js

@@ -65,7 +65,7 @@ TreeTransformer.prototype = new TreeWalker;
                     x = this;
                     descend(x, tw);
                 } else {
-                    x = this.clone();
+                    tw.stack[tw.stack - 1] = x = this.clone();
                     descend(x, tw);
                     y = tw.after(x, in_list);
                     if (y !== undefined) x = y;