general: Proof of concept wayland support.

This is a proof of concept wayland support.

It includes three libraries which really should not live here.

* x11-base/xorg-server-1.15.99.902
* x11-proto/fontsproto-2.1.3 - required to make xorg-server build.
* dev-libs/libinput - required for wayland input.

IMPORTANT: wayland support for git master currently cannot be disabled
           https://bugzilla.gnome.org/show_bug.cgi?id=728185

Installing this means that you have to have the wayland USE flag enabled,
otherwise the build will FAIL.
This effects x11-wm/mutter-9999

The majority of these changes are inspired by
https://github.com/Heather/gentoo-gnome/commit/dc83fffb914665a8733c8fbeb3ba91efe997ac0a

Notable small fixes.

* gnome-base/gnome-shell-9999: EGIT_HAS_SUBMODULES not set but should be.
* cogl/cogl-9999: No longer has Makefile.in
* x11-wm/mutter-9999: Multiple DOCS files have been removed upstream.