thumbs, jp2, autocrop for image N before doing N+1

[danh]

We create thumbnails, jp2s, and autocrop a set of images.

This could be done in two ways:
(1) first create all the thumbs, then all the jp2s, then all the autocrops
    or
(2) create thumb for first image, then jp2, then autocrop, then do the second image, then the third, etc

We are going along the first path for expediency.

But Hank points out that the second path would give the os a much better chance of keeping the images in memory (3 reads of the same file near the same time will be be much easier to do).

So we should unroll our 3 loops, and reroll along path 2.