patch applied (ghc-6.8/ghc): install the Cabal docs, and make them show up in a binary distribution

[Simon Marlow]

Fri Oct 26 05:24:56 PDT 2007  Simon Marlow <simonmar at microsoft.com>
  * install the Cabal docs, and make them show up in a binary distribution

    M ./Makefile -2 +3
    M ./distrib/Makefile +1
    M ./mk/install.mk -5 +9