Improving a function `presize` using new parameter `photoRealSize`

Hello.

In our current project we faced with the problem: our cropped image had css property `width` and the function `presize` could not properly count a real width of the image. Therefore, scale parameters also was incorrect (in our case they equals 1 instead of a value about 4).

I added a new parameter `photoRealSize` for improving the `presize` function.

Look the commit. For example, we used this parameter like this:

```coffeescript
@.initCrop = ->
  img = new Image()
  img.onload = ->
    w = @width
    h = @height

    $("#img").Jcrop {
      boxWidth : 600
      aspectRatio: 4.0/3
      bgOpacity: 0.3
      photoRealSize: [w, h]
      minSize: [200, 150]
      addClass: 'jcrop-dark'
      onSelect: setCoords
    }, ->
      setBounds(@)
      return

    return

  img.src = $("#img").attr("src")
  return
```

If this parameter will not be specified, we will have old behavior of the function `presize`.

Thank you for your job!