patch applied (packages/Cabal): Cope better with ghc bug #2201, display a better error message

[Ian Lynagh]

Mon May  5 01:57:46 PDT 2008  Duncan Coutts <duncan at haskell.org>
  * Cope better with ghc bug #2201, display a better error message
  Otherwise it can (and does) really confuse people.
  The problem is that the command $ ghc-pkg-6.9 describe '*' --user
  returns a non-zero exit code if the user package db is empty.
  ghc-pkg intends this exit code to tell us if the query returned
  any results (one can use more complex queries as tests) but Cabal
  interprets it as failure. Indeed we cannot distinguish it from
  any other kind of failure from ghc-pkg.

    M ./Distribution/Simple/GHC.hs -1 +11

View patch online:
http://darcs.haskell.org/packages/Cabal/_darcs/patches/20080505085746-adfee-30b21f3f434bdf43f0dea4fe3d1baf5c8f33006d.gz