Don't draw the entire world on a giant surface.

Breaks the minimap!
Who wants to walk in circles? I do!

ModDict only works for [], not get()/set()
Remove redundant 'Map' dict.

Add 'explored' field to Cell instead, use RealMap for everything.
Prevent loonies from causing an int overflow by travelling millions of tiles
merged
copy from github (yuk)
merged in cell copying fix
Merge pull request #2 from FLHerne/master

Use copy.copy, rather than messy constructor.