Add two extra anvils to the special weapons shop

The single anvil was breaking in some games.  This ensures that both
teams will always have an anvil available.
Remove fences in front of shops

People sometimes drop items over the shop fences.  The only reason for
having them there is to 'protect' the villagers.  However, the villagers
are invunerable and move back into position whenever pushed.
Add clean task to rakefile