Snapshots of cairo and glitz for mozilla usage.

We only include the relevant parts of each release (generally, src/*.[ch]), as
we have moz.build files used by the Mozilla build system. For documentation and
similar, please see the official tarballs at http://www.cairographics.org/.

VERSIONS:

  cairo (1.18.4)

==== Updating and Patching Cairo ====

To change Cairo in Mozilla Central:

- Make your changes to `gfx/cairo/cairo`, and test as necessary.

- Add an appropriate patch to `gfx/cairo/patches`, and edit the
  `patches` list in `gfx/cairo/moz.yaml` to apply it at the
  appropriate point in the list --- typically the end.

- Test that UpdateBot can actually reconstruct the vendored Cairo
  sources with the following command:

      mach vendor gfx/cairo/moz.yaml -r $REVISION --patch-mode check --force

  where `$REVISION` is the `revision` currently listed in `moz.yaml`.
  UpdateBot should say that the "upstream hasn't modified files
  locally", and `git status` should be clean.

- Submit a patch for review that includes both the changes to
  `gfx/cairo/cairo` as well as the changes to `moz.yaml` and the new
  patch file in `gfx/cairo/patches`.