toDataUrl multiplier not applied to shadow's values

[ghost]

Version

1.6.1

Test Case

http://jsfiddle.net/yfzv4x87/

If you are on retina screen then you must scroll all the way to the bottom right in jsfiddle render. The image is very large on retina. Not so big on 1:1 pixel ratio screen.

Screen shot of jsfiddle:

On top is canvas, on bottom is img. Notice shadow in img.

Steps to reproduce

1. Create textbox with shadow
2. Take toDataUrl of textbox with multiplier of 5
3. Insert data url into image

Expected Behavior

Image's shadow matches canvas shadow

Actual Behavior

Image shadow appears less offset and less blurred than canvas original

Screen shot of canvas:

Screen shot of image, after multiplier applied to data URL:

[asturur]

https://github.com/kangax/fabric.js/blob/master/src/mixins/canvas_dataurl_exporter.mixin.js#L128

Problem is here.
html canvas never scale the shadows. We scale the shadow keeping track of the multipliers from canvasZoom and objectZoom and retinaZoom.

When we set a direct ctx.scale() like that we fail at recovering it later when is time to render the shadows.