No more overflow

Handelabra has now protected the game against overflow and underflow errors.  No longer can you give AZ 2 billion health.  I am both slightly sad and rather gleeful, because I'm guessing that this is almost entirely my fault.  :D  

There are still some weirdnesses when you reach that level of damage, though.  Damage modifiers can push the damage negative, and AZ refused to heal from Null-Point. The log claims that he was at maximum health (he was as far from maximum health as possible), but I think the problem was the negative damage amount.