game: Clean up output of get_road_length_value().
game: Rename players_init() (from reset_player_settings())
pathfinder: Only allow connection to flag if it is the end point
building: Use resource_type_t for stock
Clean up handling of updates to building stock.

Remove index lookup tables, and instead use the type field of the building stock to find the correct entry to update.
Fix a bug where a resource scheduled to unknown destination would not update the requested number of items.

This bug only affected buildings using RESOURCE_GROUP_FOOD (i.e. mines) because the local variable "res" was not merged into RESOURCE_GROUP_FOOD before the check. This caused a problem of mines receiving unlimited amounts of food.