display: Split out rotation sanity checking

https://bugzilla.gnome.org/show_bug.cgi?id=731166
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
display: Move apply_rotation_to_geometry()

https://bugzilla.gnome.org/show_bug.cgi?id=731166
display: Fix problems when left-most monitor is rotated

When rotating the left-most monitor, we could end up with one
of two scenarios:
- Huge gap between monitor one and two when the left monitor is made
to be vertical
- Monitor two overlapping on top of monitor one when monitor is
back to being horizontal.

In addition to adding a bit more debug, we now take the old and new
rotation of monitor one into account when calculating the moving
screen edges.

https://bugzilla.gnome.org/show_bug.cgi?id=731166
display: Remove shadowing variable

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