Merge remote-tracking branch 'origin/darwin-clang-stdenv' into staging

Conflicts:
	pkgs/applications/editors/vim/macvim.nix
systemd: Update to 217
Set SDKROOT etc. in stdenvNative

Fixes a build failure in gawk with Xcode 6.1 on 10.9.
Hack to fix libc++abi build
xorg-server: major bump 1.14.* -> 1.16.1 (incl. deps)
boost: Add optional Boost.MPI support

Boost.MPI is a C++ interface library to the
message passing interface (MPI) standard.
fontconfig: patch and document
Merge recent master into staging

Nixpkgs Hydra: ?compare=1157272

TODO: port e22889064f82be3

Conflicts:
	nixos/tests/gnome3_10.nix (auto-solved)
	pkgs/applications/video/aegisub/default.nix
	pkgs/development/libraries/boost/1.55.nix
gst-plugins-bad: enable gl plugin (close #4763)
findTarballs: Take nullglob into account
Die tabs die
findTarball: Handle pipefail

It was failing because the bash subshell died with SIGPIPE, which is
no longer ignored.

http://hydra.nixos.org/build/16766452
Merge remote-tracking branch 'origin/master' into staging

Conflicts:
	pkgs/stdenv/generic/default.nix
mesa: Don't depend on Wayland

NixOS currently does not have any Wayland support, so it's kinda
pointless ATM to make everything depend on it.
nixBuild: Respect the preHook/postHook of the caller
Fix running preHook

Accidentally (?) lost in e3875297fac671f20feb803306e7c55789ac749e.
stdenv: Statically include the default build inputs

Otherwise, stdenv won't have a reference to e.g. patchelf on Linux
(because it was passed in by mkDerivation). This causes the installer
tests to fail, because having "stdenv" in the installation CD closure
is not enough to pull in all stdenv packages.

http://hydra.nixos.org/build/16546643
stdenv: Remove propagatedUserEnvPkgs

Stdenv is not really intended as an installable package. Nowadays it's
much better to use "nix-shell -p" to get a build environment.
Fix stdenv allowedRequisites check

It has to include the default build inputs now (like
"compress-man-pages.sh").
Revert "ruby: Fix build on systems with store optimisation. Closes #4273. #4266 promises a better fix."

This reverts commit d2c0011c2fafa92624b30a2408123a15a1af390f.

c04e49289871232ff3c2fd1239b64c2513f18fd1 gives a cleaner solution that's
not specific to ruby.