pixman: use pixman_cairo for xorg, flatten its includes
xorg: update xorgserver to 1.13.4, and more

- update some modules to work with the newer server
- fix many other modules via overrides
- huge cleanup in overrides via better propagation
  and pixman include flattening
- URLs of XCB stuff have been moved
Merge pull request #471 from vcunat/p/xorg

xorg updates