* Modularised the xorg.conf generation. For instance, the Wacom and
Synaptics support has been moved into separate modules. The
contents of xorg.conf is defined by the option
services.xserver.config, and various other options for specific
sections (e.g. services.xserver.serverLayoutSection).
* displayManager.job.env: made this an attribute set.
* tcpEnable -> enableTCP for naming consistency.
* defaultDepth can be set to 0 to leave it undefined (needed for the
vmware driver).
* Removed some options that seem obsolete or are now the default
(e.g. RenderAccel, AllowGLXWithComposite).
* Removed services.xserver.package. This can now be done using
nixpkgs.config.packageOverrides.
svn path=/nixos/trunk/; revision=17004
