Re-write the Haskell Platform out of haskell-defaults.nix.

 1) Packages formerly called haskell-haskell-platform-ghcXYZ-VVVV.X.Y.Z are
    now called haskell-platform-VVVV.X.Y.Z. The latest version can be
    installed by running "nix-env -i haskell-platform".

 2) The attributes haskellPackages_ghcXYZ.haskellPlatform no longer exist.
    Instead, we have attributes like haskellPlatformPackages."2012_4_0_0".
    (Note that the last numeric bit must be quoted when used in a Nix file.)
    The latest Platform has a top-level alias called simply haskellPlatform.

 3) The haskellPackages_ghcXYZ package sets offer the latest version of every
    library that GHC x.y.z can compile. For example, if 2.7 is the latest
    version of QuickCheck and if GHC 7.0.4 can compile that version, then
    haskellPackages_ghc704.QuickCheck refers to version 2.7.

 4) All intermediate GHC releases were dropped from all-packages.nix to
    simplify our configuration. What remains is a haskellPackages_ghcXYZ set
    for the latest version of every major release branch, i.e. GHC 6.10.4,
    6.12.3, 7.0.4, 7.2.2, 7.4.2, 7.6.3, 7.8.2, and 7.9.x (HEAD snapshot).

 5) The ghcXYZPrefs functions in haskell-defaults.nix now inherit overrides
    from newer to older compilers, i.e. an override configured for GHC 7.0.4
    will automatically apply to GHC 6.12.3 and 6.10.4, too. This change has
    reduced the redundancy in those configuration functions. The downside is
    that overriding an attribute for only one particular GHC version has become
    more difficult. In practice, this case doesn't occur much, though.

 6) The 'cabal' builder has a brand-new argument called 'extension'. That
    function is "self : super : {}" by default and users can override it to
    mess with the attribute set passed to cabal.mkDerivation. An example use
    would be the definition of darcs in all-packages.nix:

    | darcs = haskellPackages.darcs.override {
    |   cabal = haskellPackages.cabal.override {
    |     extension = self : super : {
    |       isLibrary = false;
    |       configureFlags = "-f-library " + super.configureFlags or "";
    |     };
    |   };
    | };

    In this case, extension disables building the library part of the package
    to give us an executable-only version that has no dependencies on GHC or
    any other Haskell packages.

    The 'self' argument refers to the final version of the attribute set and
    'super' refers to the original attribute set.

 7) Haskell Platform packages always provide the Haddock binary that came with
    the compiler.

Noteworthy bits of information:

 - Haskell Platform 2009.2.0.2 is broken because of build failures in cgi and
   cabal-install.

 - Haskell Platform 2010.1.0.0 is broken becasue of build failures in cgi.
haskell-packages.nix: remove references to parsec2
haskell-wxcore: jailbreak to fix build with recent versions of array
haskell-ConfigFile: update to version 1.1.2
haskell-Glob: update to version 0.7.5
haskell-RepLib: update to version 0.5.3.3
haskell-data-lens: update to version 2.10.5
haskell-digestive-functors-aeson: update to version 1.1.8
haskell-esqueleto: update to version 1.4.1
haskell-hledger-lib: update to version 0.23.2
haskell-hledger-web: update to version 0.23.2
haskell-hledger: update to version 0.23.2
haskell-iCalendar: update to version 0.4.0.1
haskell-pandoc: update to version 1.12.4
haskell-shake: update to version 0.12
haskell-statistics: update to version 0.11.0.1
haskell-system-fileio: update to version 0.3.13
haskell-unbound: update to version 0.4.3.1
haskell-hakyll: jailbreak to allow building with network 2.5.x

https://github.com/jaspervdj/hakyll/issues/255
haskell-oeis: jailbreak to fix build with network 2.5.x