savegame: Fix broken flag transport after game load.

Important flag data was missing in save game file.
serf: Increase consumption of food by miner according to difficulty of original game.

It seems that the random chance of not requiring food should be inverted from 7/8 to 1/8, thus making it almost certain that the miner will need food before working.
game: Clean up and rename resource scheduling function using more descriptive names.
game: When routing resources to unknown destination, also take into account building that accept RESOURCE_GROUP_FOOD.

Before the search, convert any food resource type into RESOURCE_GROUP_FOOD to match buildings correctly.