This should fix ticket #120 in future which is the problem where you do
something like "sudo runghc Setup install" and you accidentally end up
using a different version of the compiler or of the Cabal lib and you get
an unhelpful error message:
> Setup.hs: error reading ./.setup-config; run "setup configure" command?
Well now you'll get a helpful error message:
> setup: You need to re-run the 'configure' command. The version of Cabal
> being used has changed (was Cabal-1.3.6, now Cabal-1.3.7).
If the compiler version being used has changed too we get the extra helpful:
> setup: You need to re-run the 'configure' command. The version of Cabal
> being used has changed (was Cabal-1.3.6, now Cabal-1.3.7). Additionally
> the compiler is different (was ghc-6.8, now ghc-6.9) which is probably
> the cause of the problem.
Of course this does not help for older versions of Cabal but there's not a
lot we can do about that.