transform function calls to IIFEs (#1560)

- expose function body to call sites for potential optimisations
- suppress substitution of variable used within `AST_Defun`

lib/ast.js

@@ -91,7 +91,15 @@ var AST_Token = DEFNODE("Token", "type value line col pos endline endcol endpos
 }, null);
 
 var AST_Node = DEFNODE("Node", "start end", {
-    clone: function() {
+    clone: function(deep) {
+        if (deep) {
+            var self = this.clone();
+            return self.transform(new TreeTransformer(function(node) {
+                if (node !== self) {
+                    return node.clone(true);
+                }
+            }));
+        }
         return new this.CTOR(this);
     },
     $documentation: "Base class of all AST nodes",