See #490 discussion.
This reverts commit 1278859d31, reversing
changes made to 0c020c98f9.
Conflicts:
pkgs/desktops/xfce/core/xfce4-session.nix (take master)
pkgs/lib/misc.nix (auto)
Also updated libdrm to 2.4.40 (not 2.4.41 because they have broken tars for that)
Removed the Mesa patch for sis video on mips64el-linux because sis is not
supported in Mesa anyway (since version 8)