Configure Nix package names for bz2 and crypt libraries.

Required for <https://github.com/NixOS/nixpkgs/pull/2264>.
Add post-processing hook that disables text-icu's test suite on Darwin.

https://github.com/bos/text-icu/issues/6
https://github.com/NixOS/nixpkgs/pull/2254
gtk2hs-buildtools requires 'hashtables' build input when compiling with
GHC 7.8.2. We add that package unconditionally in a post-process hook.
Added the pkglist utility, a small program that generates a Hydra CI job based
on a package.txt file as used in the Debian project.
pkglist.hs: avoid use of 'void' to fix build with old compilers
pkglist: add a doc-test
pkglist: don't hard-code paths to input and output
Automate generation of the nix expressions using a makefile.
data/haskell-packages/default.nix: Hydra doesn't seem to like the fancy 'cabal' back-reference in the arguments to this function
data/haskell-packages/default.nix: simplify things even further
data/haskell-packages/default.nix: hard-code system as 64-bit linux
pkglist.hs: merge changes to default.nix back into the program
pkglist.hs: improve the algorithm that distinguishes system packages from Haskell packages in the 'build-tools' field
data/packages.txt: add alex and happy
haskell-packages: re-generate with latest toolset
data/packages.txt: sort list alphabetically and weed out duplicates I introduced earlier
data/haskell-packages: regenerate with latest software
Cabal2Nix/Name.hs: map 'bz2' to 'bzip2' and 'sane-backends' to 'saneBackends'
Cabal2Nix/PostProcess.hs: libcrypt is part of glibc
haskell-packages: regenerated with latest software