fixed pixel ratio issue with buffer canvas usage

src/Animation.js

@@ -214,7 +214,7 @@
             that._animationLoop();
         }
     };
-    RAF = (function() {
+    var RAF = (function() {
         return window.requestAnimationFrame
             || window.webkitRequestAnimationFrame
             || window.mozRequestAnimationFrame

src/Shape.js

@@ -229,6 +229,7 @@
                 stage, bufferCanvas, bufferContext;
 
             if(drawFunc && this.isVisible()) { 
+                // if buffer canvas is needed
                 if (this._useBufferCanvas()) {
                     stage = this.getStage();
                     bufferCanvas = stage.bufferCanvas;

src/Stage.js

@@ -617,7 +617,12 @@
             this.content.className = KINETICJS_CONTENT;
             container.appendChild(this.content);
 
-            this.bufferCanvas = new Kinetic.SceneCanvas();
+            // the buffer canvas pixel ratio must be 1 because it is used as an 
+            // intermediate canvas before copying the result onto a scene canvas.
+            // not setting it to 1 will result in an over compensation
+            this.bufferCanvas = new Kinetic.SceneCanvas({
+                pixelRatio: 1
+            });
             this.bufferHitCanvas = new Kinetic.HitCanvas();
 
             this._resizeDOM();