extend __PURE__ to AST_New (#2706)

fixes #2705

lib/parse.js

@@ -1225,12 +1225,14 @@ function parse($TEXT, options) {
         } else {
             args = [];
         }
-        return subscripts(new AST_New({
+        var call = new AST_New({
             start      : start,
             expression : newexp,
             args       : args,
             end        : prev()
-        }), allow_calls);
+        });
+        mark_pure(call);
+        return subscripts(call, allow_calls);
     };
 
     function as_atom_node() {