This fixes regression CORE-16289 where we could not longer
move the taskbar at a different than default location,
as WindowSnap would interfere.
Many Thanks to the patches author Doug Lyons.
Eventually the heuristic that we use here to identify the
taskbar via used window-styles could be improved later.
Theoretically possible that it bails out on some other windows.
The regression was introduced by 0.4.12-dev-373-g
7e396787ed
patch is a backport from master 0.4.13-dev-962-g
4193b8d8ac