small changes in cursor behaviour.

the selection box will now disappear when the cursor moves over the control
panel, in an effort to reduce accidental misclicks.

the selected unit arrow will no longer be occluded by ANYTHING.
i think this is some sort of falling code.

it looks as though there's a bunch of other stuff in there too..
i kinda remember something about weird pathfinding when going up stairs,
oh yeah, and i think i streamlined something so that it doesn't iterate
for large units.

not sure, pretty tired. leave a message on the forums to let me know what
i broke.
another fix for reapers.
!= != ==