Fixed|World|SectorCluster: Dynamic map-hacks depending on non-neighbor planes

For example, the Red Key trap in Alien Vendetta MAP04 uses a map-hack
construct where the columns are dependent on the Planes from both the
column sector and the adjacent neighbors. Both planes must be observed
in order correctly resolve the "current" dependent plane when a move
occurs.

Also fixed a potential crash given a malformed BSP, where many nested
"selfreferencing" map-hacks might result in leafs being assigned to
the wrong Sector (which will confuse SectorClusterCirculator).