Killing a couple birds with one stone: convertRectToBase and convertBaseToScreen are deprecated and generate warnings when building against the 10.10 SDK. Furthermore, while looking into this I noticed the Quick Look starting frame was messed up on Retina based Macs, presumably due to the fact that the origin is derived from converting from base to screen, but no attempt is made to account for the (also now deprecated) userSpaceScaleFactor. I think that realistically, userSpaceScaleFactor will always be 1.0 on 10.6 unless somebody is hacking around with Quartz Debug. So a good fix for the long term seems to be to assume we will use the modern methods whenever we are running on 10.7 or higher, and to stick to the old method that should work well enough when we are on 10.6.
Merge branch 'retina-fix' into iMediaSandboxing