Add a function "fetchzip"

This function downloads and unpacks a file in one fixed-output
derivation. This is primarily useful for dynamically generated zip
files, such as GitHub's /archive URLs, where the unpacked content of
the zip file doesn't change, but the zip file itself may (e.g. due to
minor changes in the compression algorithm, or changes in timestamps).

Fetchzip is implemented by extending fetchurl with a "postFetch" hook
that is executed after the file has been downloaded. This hook can
thus perform arbitrary checks or transformations on the downloaded
file.

(cherry picked from commit c8df88885891bdb6d1f207cf203e4b0af48d5486)

Conflicts (using fetchzip now):
	pkgs/tools/networking/dd-agent/default.nix
Add a utility function "fetchFromGitHub"

This is a small wrapper around fetchzip. It allows you to say:

  src = fetchFromGitHub {
    owner = "NixOS";
    repo = "nix";
    rev = "924e19341a5ee488634bc9ce1ea9758ac496afc3"; # or a tag
    sha256 = "1ld1jc26wy0smkg63chvdzsppfw6zy1ykf3mmc50hkx397wcbl09";
  };

Conflicts (simple):
    pkgs/tools/networking/dd-agent/default.nix

This is a squashed cherry jam:
    ebd8573046dee7d76fab1da3859e7480b716ee03
    6aeb59bbe0e5a90017be3350e519ec818d675a0d
    ea36f3b86892263d172fa3d0d0d4ae00d82a0edc
Merge #2630: add and use fetchpatch

fetchpatch is fetchurl that determinizes the patch.
Some parts of generated patches change from time to time, e.g. see #1983 and
http://comments.gmane.org/gmane.linux.distributions.nixos/12815
Using fetchpatch should prevent the hash from changing.

(cherry picked from commit 137eae0b55949bcfd6a2f4ba12964db8bdfae954)

Conflicts (simple, patchutils version from master):
	pkgs/development/libraries/haskell/gitit/default.nix
	pkgs/tools/text/patchutils/default.nix
mupdf: fix patch hash by fetchpatch

Thanks to @kirelagin for reporting on IRC.

(cherry picked from commit f77e2dcb387637aea3a304c404867d27f91bccb8)
fix mkpasswd: use the git repository

Signed-off-by: Austin Seipp <aseipp@pobox.com>
(cherry picked from commit e5eed8f664891e7337c1c70a654930617da4247b)
Note recently this was picked and reverted because of missing dependencies.
update lib/maintainers.nix from master