Region pointers were considered a scalar type, so compare_scalar_type would
get called to compare region pointers in trans. This would fail, since
compare_scalar_type has no case for region pointers.
Changed type_is_scalar to return false for region pointers. This had the side
effect of breaking casts to types of the form &T. To ameliorate that, I added
library functions ptr::assimilate (taking a &T to a *T) and ptr::to_uint
(taking a &T to a uint), both of which use reinterpret_cast.
While I was at it, I removed ty::type_has_resources, which is dead code.
