Makes farmers farm crops.
Villagers: Farmers can also harvest carrots and potatoes.
E_BLOCK_POTATOES isn't an solid block. Villagers were floating above them.
Villagers don't look for new crops when they already found one.
Slight cleanup.
Villagers: Fixed only gettings the crops block when farming.
Villagers: Farmers now replant the crops.
Added GetCropsPos and DidFindCrops functions.
Villager: Farmer: Crops finding is more random.
Fixed compiler error.
SIGABRT exits with failure.
Updated polarssl
Villager: Farmers can't place crops on blocks other then farmland.
Villagers: Harvesting is more rare.
Rewritten networking to use non-blocking sockets.

This fixes #592.
Fixed Linux compilation.
Cleanup
Most code in Tick is now split up in different functions.
Squashed common code.
Villager: Few more comments.
The world can now be configured wether farmers should be able to harvest crops.
Villager doesn't check the environment for crops if it doesn't need to.