patch applied (packages/Cabal): Make an Arch enum like we have for OS and use it

[Ian Lynagh]

Tue Mar  4 12:38:02 PST 2008  Duncan Coutts <duncan at haskell.org>
  * Make an Arch enum like we have for OS and use it
  We get more robust parsing and comparisons of arch names this way
  and it'll allows us to detect and warn about unknown arches.

    M ./Distribution/PackageDescription.hs -3 +3
    M ./Distribution/PackageDescription/Configuration.hs -6 +6
    M ./Distribution/Simple/Configure.hs -3 +3
    M ./Distribution/System.hs -10 +62

View patch online:
http://darcs.haskell.org/packages/Cabal/_darcs/patches/20080304203802-adfee-a3a00b42d44d44ad8f17d95d9ecc79fa3b10deba.gz