fixes for multi-screen behavior

--fix wrong placement at multi-screen environment
during startup. freeEdges function was not sufficient for
reconsiderScreen() because there was a chance to
exclude edges that even though they were available
it returned fault results. Such case is when
a view request available edges for specific screen
and the edge of that specific view is also exluded
because that view has not finished its movement
to the new assigned screen.

--fix re-adding an explicit dock when its screen
is activated. A check was missing in order to
confirm that a primary dock is occuping that
edge but we must check also that the primary
screen is the same with the explicit one.

--add/improve debug messages

(cherry picked from commit 0bab3446)

BUG: 399456
FIXED-IN: 0.8.2