display: Check whether the rotation changes when relayouting

Consider whether rotation has changed when checking whether
we need to relayout the screens. Before, we would only have changed the
layout if the resolution changed.

This doesn't fix the problem of the relayouting code not taking rotation
into account, but it will at least allow us to run that code when only
the rotation changes.

https://bugzilla.gnome.org/show_bug.cgi?id=731166