LZMA update plus several ZScript improvements.
TVector2 (const TVector3<vec_t> &other)
* This narrowing constructor was causing a problem with a `clamp()` overload in the next commit. * Believe this is a product of a by-gone time before we had the `XY()` method on `TVector3<T>` objects.
This had already been agreed by all involved authors, but apparently not all files were changed accordingly.
