how to cabal-install with ghc-8.rc3 ?

[Johannes Waldmann]

Hi.

I would love to test rc3. Building (with 7.10.3)
from source went fine. But then I cannot cabal-install anything:

random-1.1: installed package info from too old version of Cabal (key field
does not match id field)
Failed to install random-1.1

What is the recommended upgrade path?

( bootstrap.sh in cabal/cabal-install (current from github)
does not work, tries to download a Cabal version that's not on hackage )

Thanks, J.W.