[PATCH 4 of 4] rust-cpython: mark unsafe functions as such

[Augie Fackler]

On Sun, Sep 01, 2019 at 08:46:07PM +0200, Raphaël Gomès wrote:
> Thanks a lot for this series, it looks very good to me.
>
> There was indeed a lot of room for improvement.

Queued per this review, thanks.