patch applied (cabal): Make lack of language extensions an error not a warning

[Duncan Coutts]

Wed Dec 16 12:45:05 PST 2009  Duncan Coutts <duncan at haskell.org>
  * Make lack of language extensions an error not a warning
  Also improve the error message somewhat

    M ./Distribution/Simple/Configure.hs -3 +5

View patch online:
http://darcs.haskell.org/cabal/_darcs/patches/20091216204505-adfee-ce68c746e3f1c7e17bcaeb01102be09aeff1e475.gz