Improve parser error reporting in `ghc-pkg`
Here's what I was confronted recently due to a broken sandbox environment:
$ cabal info parsec cabal: ghc-pkg: Data.Binary.Get.runGet at position 9583: demandInput: not enough bytes
The main problem is that this message is not very helpful (other than telling that
ghc-pkg wasn't able to do something). Duncan told me, that the recent
binary API now provides better facilities for error reporting. That could be used to improve the UI of
ghc-pkg when reporting errors.