have ghc-pkg print less useless info when registering

[duncan]

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.

[igloo]

This sounds easy, let's do it for 6.12.1.

[igloo]

ghc-pkg now has a verbosity flag, and at verbosity level 0 it won't print those messages.