EvView: render correctly on hi-dpi displays

Make EvPixbufCache generate surfaces with extra resolution based on
gtk_widget_get_scale_factor(). Handle cairo surfaces with a device
scale in ev_view_draw(). Trigger an update of the pixbuf cache when
the scale factor changes.

https://bugzilla.gnome.org/show_bug.cgi?id=723431
Delete test directory.

Tests have been broken since gtk3, and we are adding updated
tests soon.
EvPixbufCache: Handle backends that don't render a selection

Handle the case where ev_selection_render_selection() doesn't actually
render a surface - this happens when a backend doesn't implement
render_selection().

https://bugzilla.gnome.org/show_bug.cgi?id=723431
Remove the configure option for tests since we don't have tests anymore
Remove test/Makefile from configure.ac

We don't need to generate it anymore.
EvPresentationView: Render correctly on hi-dpi displays

Create rendering jobs with a scale that incorporate the scale factor of
the widget, and then use cairo_surface_set_device_scale() to make the
resulting surfaces render at the correct size. Handle changes to the scale
factor both for the cached surfaces, and also for the monitor dimensions,
which are reported in scaled coordinates.

https://bugzilla.gnome.org/show_bug.cgi?id=723431
configure: Don't check for gail anymore

It's no longer used.