ledger-2.6.3: update location of the source code tarball

The source code tarball we used to rely on has disappeared.
ledger-2.6.3: update the location of the source code tarball some more

I found the original tarball at a different URL. This one doesn't
require Autoconf et al to compile.
openjade: Use default gcc
gwt: Remove obsolete version
modutils: Remove

This package is long obsolete.
xfig: Use the default gcc
ov511: Remove

This is very obsolete (last updated for Linux 2.6.0-test4).
pkgs/build-support/native-darwin-x11-and-opengl: lift native X11 and OpenGL implementation from Darwin into the Nix store
all-packages: redirect 'x11' attribute on Darwin to the native implementation
all-packages: redirect 'mesa' attribute on Darwin to the native implementation
all-packages: redirect 'freeglut' attribute on Darwin to the native implementation
xfig: update download location of the Debian patch files
git: adding an option not to build the manual

asciidoc+xsltproc take hours to run
JSON::Any: Pull in JSON
Updates related to VAAPI/VDPAU

Making ffmpeg link to libva.
Add the vdpau driver for vaapi.
Adding the vaapi Intel driver.

I also renamed the vdpau driver to 'vaapiDriver' in all-packages. I think
it's a better name.
cups: Don't build on Darwin
kde-3: Remove

KDE 3 hasn't built in a long time.  Also remove six, the only package
with a dependency on KDE 3.
linux-2.6.32-xen: Remove

Hasn't built in a long time and is obsolete anyway.
openoffice: Remove

It's superseded by LibreOffice and doesn't build anymore.