Slicing an 8192x8192 image made folder structure off-by-one for openseadragon

[patricksurry]

I used a square input file of exactly 2^13, and sliced with no command-line arguments. I got a file structure with folders 0...14, with a 128x128 image in 8/ and a single 256x256 image in 9/. Openseadragon seemed to expect that the image in 8 would be 256x256 and 9 would contain four tiles. I "fixed" by hacking the .dzi file to say the full image size was 8193x8193, or (better!), by removing folder 0/ and renaming all the other folders n/ => n-1/