popover: Only give back focus to drawable widgets

If the previous focus widget is not drawable anymore, don't even
bother in transmitting the focus grab to it.
popover: Track toplevel focus changes

Make the popover temporarily undo the GTK+ grab, so it remains modal
to its window, but does not attempt to steal focus on other non-modal
windows that get the focus.

This was most confusing with keyboard navigation, as the focus would
remain stuck on the popover, and not move to the newly focused window
after the popover was dismissed. It didn't have as much effect on
pointer operations as only the first click would be consumed in order
to hide the popover.
popover: Track toplevel's focus widget when visible

If the toplevel focus widget is forced out of the popover (eg. through
gtk_widget_grab_focus() anywhere else), then dismiss the popover.
Allow selecting a dark variant with GTK_THEME

Dark themes need to be debugged, too.

Author:    Matthias Clasen <mclasen@redhat.com>
calendar: grab focus first, emit signals after

It may be unusual, but handlers of day-selected may want to transfer
focus somewhere else, without getting it reset back right after by/to
the calendar. This makes popovers demo work on the calendar again, for
one...
tests: fix testcalendar

Missing argument in gtk_style_context_get(), fooled by varargs.
Improve GtkStack documentation

As has been pointed out in
https://bugzilla.gnome.org/show_bug.cgi?id=725711
it is a little confusing that we have the concept of
a visible child and of the child being visible itself.
entry: use priv->dnd_position when rendering the DND cursor

This makes "cursor position" track the DnD point again, looks much
more intuitive than just rendering it on the pre-DnD position.

https://bugzilla.gnome.org/show_bug.cgi?id=725866
entry: Make DnD coordinate calculation compensate for entry icons

This made DnD have effect farther on the left when dragging text over
any entry with icons in it.

https://bugzilla.gnome.org/show_bug.cgi?id=725866
Fix font size when gdk_x11_display_set_window_scale() is used

We have a hack in the XSETTINGS code to substitute gtk-xft-dpi
with gdk-unscaled-dpi unless the screen has a fixed window scale,
in which case we just use gtk-xft-dpi.

But if the screen is changed to have a fixed window scale, then
the substituted value of gdk-unscaled-dpi will stick around until
the next (coincidental) change to XSETTINGS. To fix this, force
an immediate reread of the XSETTINGS property when
gdk_x11_display_set_window_scale() is used.

https://bugzilla.gnome.org/show_bug.cgi?id=725754
window: Turn popovers into internal children

It turns out popovers are already smart enough to cope with this
situation, so let popovers be internal children so things that rely
on gtk_container_forall(), like DnD, work without modifications.

https://bugzilla.gnome.org/show_bug.cgi?id=725727
Updated Korean translation