Re: 4.8 docs build error

Re: Dave Page 2019-06-05 <CA+OCxoz4ujskbnAC84d5QvPpBtg-sLcvwqD5ZmrA_5_MsSK9hA(at)mail(dot)gmail(dot)com>
> This just works around the problem, and will result in incomplete docs. The
> correct solution is to ensure that you have the application dependencies
> installed in the environment in which you build the docs (it's actually a
> subset of them - you probably just need to add the cryptography module).

Thanks Dave, that fixed it.

We already had almost all python runtime dependencies mirrored as
build-dependencies, but python3-crypto{,graphy} was indeed missing.

Will look at the other issue now and then update the package.

Christoph