New better way of identifying packages.

From now on, binary wrappers explicitly have to write out the nixpkgs
version used to install the package, the package name (attrpath), the
derivation hash and the out hash.  This makes it possible to
build (and verify) the package even if it gets deleted from the binary
cache on nixos.org.
coqtop
TODOs.
firefox: pulseaudio support.
Added jbig2.
techtalk abstract
README.org translated to English.
README.org formatting made compatible with github.
Zsh compatibility.
Exclusion support.
proof-general.
firefox 18.0
android sdk: adb, fastboot
Refactor ghc (and related) binaries handling
Bump ghc version to 7.6.2
Download nixpkgs snapshots from github instead of nixos.org.
packages/: new directory for DRY programming.
ChromeOS vboot_reference added (cgpt, vbutil_kernel).
Merge branch 'master' of github:errge/ceh
firefox.nix: moved to packages/