Both branches have quite a lot in common, so it's time for a merge and
do the cleanups with respect to both implementations and also generalize
both implementations as much as possible.
This also closes#1876.
Conflicts:
pkgs/development/interpreters/lua-5/5.2.nix
pkgs/development/libraries/SDL/default.nix
pkgs/development/libraries/glew/default.nix
pkgs/top-level/all-packages.nix
aszlig
c7bac81c66