Image sequence and "retina display" image names

[smvilar]

If you have an image sequence, for example:

image1.png
image2.png
image3.png

And you have also the "retina display"-named version of them, too:

image1.png
image1@2x.png
image2.png
image2@2x.png
image3.png
image3@2x.png

The image sequence algorithm assumes that the double-sized images are also part of the sequence.

A possible solution can be to modify the regexp in Utils.find_assets_image_sequence to also match the extension (i.e.: /image\d\b\..+); but it will always ignore the retina-display images.
I don't know the rest of the code well enough to understand what the best solution should be.