Make field's symbol "_" to better differentiate them from rocky.
Move stuff around.
Interface::set_menu() ALWAYS sets cur_mode to IMODE_MENU unless we're "changing to" the already-open menu (and hence closing it).  This fixes weirdness like being able to hit map-view-mode commands while a menu is open.  Also, add an ad-hoc debug key (*).  Right now, it displays the code for the current mode.
Rename mason to masonry.  Make it employ peasants, not merchants (since cutting stone is largely unskilled labor).
New function, City::get_pure_buildings(), returns a vector of Building pointers that excludes all area-derived buildings.  New function, City::get_food_cap(), returns the maximum amount of food we can store.  Right now, it's enough to feed all citizens for 10 days (assuming food goes bad after 10 days).  Might want to add options to change that in the future.  City::do_turn() checks if we've exceeded our food cap, and removes excess food if so.
The Minister of Food now displays the food cap.  Food stored is color-coded to indicate if it has, or is about to, reach the cap.