sudo: allow adding extra configuration options to the bottom of sudoers

from sudoers (5):
When multiple entries match for a user, they are applied in order.
Where there are multiple matches, the last match is used (which is not necessarily the most specific match).
add qemu-2.1

Conflicts:
	pkgs/top-level/all-packages.nix
spice: 0.12.4 -> 0.12.5
spice-protocol: 0.12.6 -> 0.12.7