9db492de6d
The only real reason we need `butspacetype` is while switching areas, where we need to delay the actual switch to the RNA _update callback since only there we can access context. So instead of trying to sync it with `spacetype`, only set while needed and unset it afterwards (as in set to `SPACE_EMPTY`). This should also allow us to re-use `butspacetype` in versioning code when trying to read removed editors. It'll store the space type value of the removed editor which we can then use on versioning. For backwards compatibility, we store `butspacetype` with the value of `spacetype`.