GNOME Shell and Mutter Prepare for the Final Release of GNOME 3.18 with Bugfixes

Mutter 3.18 Release Candidate adds support for scaling cursors on HiDPI screens, fixes a bug with the key state on FocusIn that occurred when running nested, no longer hardcodes card0, instead it now finds the right DRM device, and it won’t ignore background colors of wallpapers that do not fill the screen. There’s also code cleanups and miscellaneous bugfixes. On the other hand, GNOME Shell 3.18 Release Candidate fixes a race that occurred when attempting to load multiple background animations.