portal: combating the space-detection issue.
what needs to be tweaked next is how far away objects are spawned.
it should either be a trial&error adjustment or depend on the object's moving direction and the portal's angle in order to avoid issues with box collisions.
if the spawn distance to the portal is just a fixed value (as it was before this patch) or a constant factor (it is now) it can be too big for "nice" portal angles (in tight gaps with still enough space, but -> denied) and too small for bad angles (box collision esp. on big objects like barrels -> denied)
