More class loading performance improvements.
I fixed the newish class loading so that it correctly handles all array types.
I also removed the old code for checking if a type is illegal, which was slow and on a common path but doesn't seem to be needed anymore (although it's just commented out in case I'm wrong).  This allows me to remove the old code that pre-loaded types, which did more work that necessary.
More performance improvements.
Made the Method -> IMethod conversion faster (and use the correct API) and cache its results since it's still a bit slow.