Fix a segfault in AI_city::add_pastures().
Make a comment more clear.
In City_map::generate(), rename the vectors we pass in to make it more clear what they are.  When altering terrain chances for coastal maps, include icy hills, icy mountains, and jungles.  Make it MUCH less common for an animal to appear despite not being assigned by the world map.  In Map_tile::get_max_hunting_output(), reduce food output for dangerous animals.