This should provide a more helpful failure when people
try an unsupported GHC. We don't actually know if 7.1.x will work
or not for any x, but might as well be optimistic given it's a
development version.
1 patch for repository http://darcs.net/releases/branch-2.5:
Wed Jan 5 08:16:34 GMT 2011 Ganesh Sittampalam <ganesh@earth.li>
* record the GHC requirements in the cabal file