Bug 396853 - [ViewMgmt] No longer possible to make a part visible
without activating/forcing focus on it

If we're making a part visible and it's in the same stack as the active
part, we make the part the active part (Eclipse4 behaviour).  This makes
sure we don't re-activate the already active part (causing a spurious
setFocus call).


Change-Id: I4099ff3c30664a5b5ef3fdaec939f500a7fe4bbd