Skip focus tests in make check

These require a window manager to work, and we currently don't
run one when we run make check tests under Xvfb.
reftests: Make textview-margins pass in make check

I found that setting margins to zero makes the textview clip
away some overshooting pixels. So, instead of a 0/10 split,
do this test with a 2/8 split of margins, to avoid the clipping
issue.
GtkToolbar: Set clip

This allows outset box shadows to work on toolbars.

https://bugzilla.gnome.org/show_bug.cgi?id=734526
wayland: Remove overly complex cursor cache
Fix animation-direction reftest

This was another victim of clipping changes - the labels were
overdrawing each other, leading to test failure. Prevent this
by separating the grid columns.
Update DISTCHECK_CONFIGURE_ARGS

The --disable-rebuilds option does not exist anymore, so remove
it. At the same time, add --enable-installed-tests.
Fix reftests for builddir != srcdir

Make gtk-reftest consult the REFTEST_MODULE_DIR environment
variable to find out where to look for modules, and fix the
libtool hack to construct the .libs subdirectory correctly.
3.13.6
Bump version
treeview: Check the selected node active flag before maybe starting rubberband

This check used to be present in the pre-gestures code, but was unintentionally
removed when splitting code into drag/multiclick gestures. The policy used to
be that if clicking happened on an already selected node, DnD would happen
instead of rubberband selection, so this behavior is resuscitated.

https://bugzilla.gnome.org/show_bug.cgi?id=734143
Reconstruct a missing file

Sadly I had forgotten to add selectionmode.ui to git.
Here is a reconstructed version that seems to work.
widget-factory: Turn off focus-on-click for notification close button

... because that is what most applications are doing. So lets do the
same thing for the sake of consistency and setting a good example.

https://bugzilla.gnome.org/show_bug.cgi?id=734614
widget-factory: Add a reset button to the notification

Change the initial value to something that is not a multiple of 3, so
that dismissing the notification on reset makes sense. Let's use 50
because that is already being used elsewhere.

https://bugzilla.gnome.org/show_bug.cgi?id=734614
build: Require libepoxy

If we want to use OpenGL in GDK then we have two choices; either:

  - find the GL headers on each platform
  - do extension discovery
  - implement all the crazy dlopen()/dlsym() dispatch tables

*or* use libepoxy, which shields us from all this madness and provides a
decent layer for GL clients to use, without creating its own namespace.

Epoxy is also used by other projects, like Xorg and piglit, and it's
portable to all the platforms GDK cares about.

https://bugzilla.gnome.org/show_bug.cgi?id=119189
Implement GdkGLContext and GdkGLPixelFormat

GdkGLPixelFormat is an ancillary class to specify pixel formats, buffer
types, and buffer sizes for GL context.

GdkGLContext is the wrapper around platform-specific GL context API.

This commit adds the base classes, and an implementation on X11.

https://bugzilla.gnome.org/show_bug.cgi?id=119189
gdk: Make GdkGLPixelFormat less smart

We use GdkGLPixelFormat only as a storage for GL configuration options.
The validation is only made when creating a GdkGLContext.

Validation for feature discovery and fallback code paths can be done
directly using gdk_display_validate_gl_pixel_format() instead.
gtk: Add a GL drawing widget

https://bugzilla.gnome.org/show_bug.cgi?id=119189
Improve documentation of GdkGLPixelFormat
gl: Add a back pointer from the window to the context

This way we can check if a GdkWindow has a GdkGLContext associated to
it.
Improve documentation of GdkGLContext