patch applied (cabal): Change installation layout on Windows slightly

[Duncan Coutts]

Fri Aug 24 09:31:41 PDT 2007  Duncan Coutts <duncan at haskell.org>
  * Change installation layout on Windows slightly
  Make Haskell part of the default $prefix and make docs relative
  to $prefix rather than $datadir which is fixed for libs.
  Make the default fixed lib $datadir be Program Files\Haskell rather
  than Common Files.

    M ./Distribution/Simple/InstallDirs.hs -20 +8