tahoe-chk in particular has a number of API incompatibilities, so also deal
with those.

If you are not using nix then you'll have to figure it out yourself, sorrrrryy.

fixes for base64 issues

we need to use an _even older_ version of ghc than we're using now and
modern-uri doesn't seem particularly amenable to that.

network-uri is perfectly fine, anyway.

reduce closure size etc

Each generated with `cabal2nix https://.../` and then mangled by alejandro