Adwaita: wide paned separator style

...paned separator decoration fixed in the process.
x11 glcontext: Always use RGBA texture format, as we use alphas
gdkglcontext-x11: Fix pixmap creation

Always use NPOT textures

https://bugzilla.gnome.org/show_bug.cgi?id=738670
wayland: don't init if XDG_RUNTIME_DIR missing

wayland doesn't strictly follow the XDG_RUNTIME_DIR spec by falling back
to another directory in case the runtime dir is not properly set.

When this variable is unset, wayland will log an error to us, which we
treat as fatal, aborting the entire program.

Skip ourselves all the trouble and don't try to bring up the wayland
backend when we know it will fail in this way.

https://bugzilla.gnome.org/show_bug.cgi?id=738873
Updated Indonesian translation