have ghc-pkg print less useless info when registering
This is just the ghc part of Cabal ticket #487, "print less useless info during builds".
Useless: Reading package info from "dist/installed-pkg-config" ... done. Writing new package config file... done. This message is generated by ghc-pkg. We should patch ghc-pkg to not be so verbose by default. That message is only needed at a higher verbosity level.
Actually what's missing is any notion of verbosity in ghc-pkg. It doesn't matter so much what the default verbosity level is as long as Cabal can tell ghc-pkg to be quiet by default. Of course we still want to know about errors, warnings etc.