Ignore antialiasing gives false positive

[NiGhTTraX]

Diffing two images with ignore antialiasing turned on gives me a false positive (the diff is blank). Images are below. Diffing them with ignore nothing or ignore colors produces the expected result.

Image 1

Image 2

Diff with ignore antialiasing

/cc @jamescryer

[jamescryer]

Colour difference tolerance is higher for the 'ignore Anti-aliasing' mode.

The quick solution to this would be to expose the tolerance settings for update https://github.com/Huddle/Resemble.js/blob/master/resemble.js#L527

Though without that tolerance the anti-aliasing detection probably won't work so well, at least with grey-scale vs color hue anti-aliasing.

The correct solution would be to use a better anti-aliasing detection algorithm. This would take some investigation. I'll have a think about it.

If you're not running the tests on different machines then it's probably safe not to use 'ignore Anti-aliasing' mode.