Fix a buffer overflow on double width fuji images

When I did the F700 support I messed up and created a buffer overflow as I allocated a widthXheight buffer and then decoded a 2XwidthXheight image into it. 

While fixing this I realized that the double width image is actually a second raw image with a darker version of the same image. This is from the fuji SuperCCD sensors that had extra pixels to expand dynamic range. There are a couple of these old fuji cameras with that support so in the future it may make sense to expose both raw files to allow dual-iso processing like in the Magic Lantern Canon 5D hack.