[dnanian]

No magic: we always try to be as conservative and careful as we can. It just involved a lot of careful benchmarks on the various methods available to copy files and selection of the best ones available to more recent OS X versions.

This kind of thing was possible because we were "cracking open" the cloner to support compression. Since we were doing something to fix a problem that was going to require significant additional testing, I wanted to make sure we offered something of additional benefit while we were all paying that price... thus, faster copying!