x11: round the scaled size *up* when we get a ConfigureNotify

Although we specify a resize increment to try and get a size that is
a multiple of the window scale, maximization typically wins
over the resize increment, so the window might be odd sized.

Round *up* in this case, rather than down, since it's better to
truncate a line or two at the bottom and right of the window rather
than have a line or two that we don't know what to do with.

https://bugzilla.gnome.org/show_bug.cgi?id=739750
x11: Keep track of the exact size in X pixels of windows

Keep track of the exact size of X windows in underlying pixels; we
generally use the scaled size instead, but to properly handle the GL
viewport for windows that aren't a multiple of window_scale,
we need to know the real size.

https://bugzilla.gnome.org/show_bug.cgi?id=739750
x11: Return the exact pixel coverage in get_frame_extents

Rather than just rounding down the position *and* the size separately
we correctly calculate a rectangle in scaled window coords that fully
covers the real window size. This really only makes a difference
when the window size/position isn't a multiple of the window scale.

https://bugzilla.gnome.org/show_bug.cgi?id=739750
Add gdk_window_get_unscaled_size

This is required for the X backend GL integration. If the
window has a height that is not a multiple of the window scale
we can't properly do the y coordinate flipping that GL needs.
Other backends can ignore this and use the default implementation.

https://bugzilla.gnome.org/show_bug.cgi?id=739750
GL: Fix GL Y coordinate flipping to use unscaled window height

This is needed in the edge case where the X11 backend rounded the actual
size, and the GL flipping really needs the correct window height to
do proper Y coordinate flipping.

https://bugzilla.gnome.org/show_bug.cgi?id=739750
GdkGLContext: Remove unused update vfunc

The update virtual function for GdkGLContext is unused and is a
leftover from a previous GL approach. Just remove it.

https://bugzilla.gnome.org/show_bug.cgi?id=739750