Support Leica GT450 scanner associated images

[nirbenor-ibex]

Solves: #297

[fiendish]

I'm curious about the "fallback" comment. Do you have older files where the subfiletype tifftag has not always been the correct way to detect this? That message from Leica says it's true for not just gt450, and I haven't found any svs files where it's not the case. So far I've been suspecting that the format spec did not actually change and that the original detection mechanism here was someone just winging it, but if you know of a machine that generates files without those tifftags that can be shared, I'd love to add such a file to my test set.

[nirbenor-ibex]

I'm curious about the "fallback" comment. Do you have older files where the subfiletype tifftag has not always been the correct way to detect this? That message from Leica says it's true for not just gt450, and I haven't found any svs files where it's not the case. So far I've been suspecting that the format spec did not actually change and that the original detection mechanism here was someone just winging it, but if you know of a machine that generates files without those tifftags that can be shared, I'd love to add such a file to my test set.

I don't have such files, so you are correct that the comment was a bit misleading, I changed how its phrased.
I chose to fallback to the previous detection mechanism as a safety measure because I couldn't find any formal spec to follow..