Read ISO from EXIF differently (similar to inside exiv2's "fixiso" setting), and hope this will be the correct way now (works for d5100 at least, please check that other ISO readouts are not broken now!)
Be a bit more regression safe:
handle standard ISO tags the same as before (however not sure if that was really correct?), and non-standard ones in the way exiv2's fixiso does
Merge pull request #147 from bluesceada/read-exif-iso-differently

Fix (for nikon d5100): Read ISO from EXIF differently (similar to inside exiv2's "fixiso" setti...