rotating phone whilst viewing a image causes nasty flashes of other images, and gets the rotation offset & scale wrong

specifically: portrait to landscape seems okay, but the rotation/scale transform is wrong when going the other way, causing nasty jumps and pops

Start by reproducing issue #1437 in the iOS image viewer, rotating from portrait to landscape and back while viewing an image. Trace the rotation and scale handling involved in that transition; done means both directions preserve the correct transform without flashes, jumps, or showing other images.

Written by the indexing model from the issue text.