Rename rendering/render_*.dart to rendering/*.dart

sky/tests/resources/display_list.dart

 
-import 'package:sky/framework/rendering/render_node.dart';
-import 'package:sky/framework/rendering/render_box.dart';
+import 'package:sky/framework/rendering/node.dart';
+import 'package:sky/framework/rendering/box.dart';
 import 'dart:sky' as sky;
 
 typedef void Logger (String s);
 
 class TestDisplayList extends RenderNodeDisplayList {
   TestDisplayList(double width, double height, this.logger, { this.indent: '' }) :
     this.width = width,
     this.height = height,
     super(width, height) {
     log("TestDisplayList() constructor: $width x $height");
@@ skipping 122 matching lines @@
   void set root(RenderBox value) {
     _renderView.child = value;
   }
   void _beginFrame(double timeStamp) {
     RenderNode.flushLayout();
     _renderView.paintFrame();
     print(_renderView.lastPaint); // TODO(ianh): figure out how to make this fit the unit testing framework better
   }
 
 }