Ok, so Chris got the default branch working on OSX again. Whew
And using diffs from his build I was able to find the probably-culprit for the OSX crash. Basically unity uses a wildly different UnityEngine.dll on that specific platform (splitting it up into tons of small dll's), and I'd just been copying the standard one over it.
Rather than break the build again, I've set up a "crazy_test" branch with a build from my machine that addresses the OSX oddity (and the System.XML vs System.Xml thing). If any of you can switch your steam install to that beta branch and test that on OSX and Linux (a quick check of windows wouldn't be bad, but it runs fine on mine) and let me know how that goes, that would be very helpful
