Fix annoying error msgs on exit.

Those sys.exit() calss were needed after all!
Stop occupied non-transparent tiles being visible.

The player's location could be determined under trees, because their
cell was marked as visible.
Draw bears and players after crossing map edges.
Partial fix for bears after crossing edges.

Bears will pursue you after you've crossed an edge,
but still can't see you across one.
Wrap player/bear coordinates at edge of map.

Rather than in middle as previously.
Player/bear co-ordinates will now always be in range(MAPSIZE).
Fix stupid typo.
Remove over-verbose debugging.
Merge branch 'FLHerne-master' into cleanup

Conflicts:
	main.py