added new clearBeforeDraw Layer property which enables you to skip canvas clearing before each draw. Added new warn() method to test suite, and added error and warning colorings to the test counter

dist/kinetic-core.js

@@ -3,7 +3,7 @@
  * http://www.kineticjs.com/
  * Copyright 2012, Eric Rowell
  * Licensed under the MIT or GPL Version 2 licenses.
- * Date: Jun 22 2012
+ * Date: Jun 23 2012
  *
  * Copyright (C) 2011 - 2012 by Eric Rowell
  *
@@ -2603,7 +2603,8 @@ Kinetic.GlobalObject.addGetters(Kinetic.Stage, ['width', 'height', 'throttle']);
  */
 Kinetic.Layer = function(config) {
     this.setDefaultAttrs({
-        throttle: 80
+        throttle: 80,
+        clearBeforeDraw: true
     });
 
     this.nodeType = 'Layer';
@@ -2717,7 +2718,10 @@ Kinetic.Layer.prototype = {
             this.beforeDrawFunc.call(this);
         }
 
-        this.clear();
+        if(this.attrs.clearBeforeDraw) {
+            this.clear();
+        }
+
         if(this.isVisible()) {
             // draw custom func
             if(this.attrs.drawFunc !== undefined) {
@@ -2738,6 +2742,25 @@ Kinetic.Layer.prototype = {
 Kinetic.GlobalObject.extend(Kinetic.Layer, Kinetic.Container);
 Kinetic.GlobalObject.extend(Kinetic.Layer, Kinetic.Node);
 
+// add setters and getters
+Kinetic.GlobalObject.addSetters(Kinetic.Layer, ['clearBeforeDraw']);
+Kinetic.GlobalObject.addGetters(Kinetic.Layer, ['clearBeforeDraw']);
+
+/**
+ * set flag which determines if the layer is cleared or not
+ *  before drawing
+ * @name setClearBeforeDraw
+ * @methodOf Kinetic.Layer.prototype
+ * @param {Boolean} clearBeforeDraw
+ */
+
+/**
+ * get flag which determines if the layer is cleared or not
+ *  before drawing
+ * @name getClearBeforeDraw
+ * @methodOf Kinetic.Layer.prototype
+ */
+
 ///////////////////////////////////////////////////////////////////////
 //  Group
 ///////////////////////////////////////////////////////////////////////