Make WebKit use libsoup 2.31.2 via deepOverride. Edit a few packages that were overridable but did not allow extra arguments. Remove a catch with deepOverride that pkgs.lib had this attribute in a different sense.

svn path=/nixpkgs/trunk/; revision=22529

pkgs/development/libraries/cairo/default.nix

@@ -4,6 +4,7 @@
 , xcbSupport ? false
 , stdenv, fetchurl, pkgconfig, x11, fontconfig, freetype
 , zlib, libpng, pixman, libxcb ? null, xcbutil ? null
+, ...
 }:
 
 assert postscriptSupport -> zlib != null;