Adjust the way monster upgrade times are calculated. [Balance]

[CIB]

Note: This is NOT a carefully tested fix to fine-tune balance. This is a very rough fix, because it is my belief that the current "balance" is way off scale. The intention is to make the game playable and enjoyable for non-veteran players. It is my belief that the people who have years of experience with this game should be expected to turn the difficulty up in the options, rather than expecting every new player to tune the difficulty down.

Rationale: The current balance makes the game a lot harder than it's supposed to be. The spawn density and general difficulty is still generally balanced for no evolution happening at all. The evolution was added to balance out the mid to late game. But as it currently stands, the effects can already kick in at day 3 (example: from a very large group of zombies, a single feral predator evolves due to the law of large numbers.. but despite this being only one zombie among many, it will cause large issues for the player as it's so fast). Once 1-2 seasons have passed, towns practically become inaccessible to non-combat oriented characters who rely on woodland survival. Furthermore, the way it's currently set up, after around 40 ingame days you will only see hulks and practically no un-evolved zombies at all.

My change ensures that at least ~10 days need to pass for the "luckiest" zombies to evolve into their highest form. The average evolution time is also increased by a high amount, meaning that with the default setting, it will only have a strong effect in the mid to late game (as was probably intended).

[Zireael07]

Why close?

[CIB]

Because I'm a derp, modified the wrong piece of code. :) Fixed version incoming soon, once I've understood the right bit of code. :P