Building base material undump script.

Based on an idea in https://github.com/peterix/dfhack/issues/119

scripts/undump-buildings.lua

@@ -0,0 +1,29 @@
+-- Undesignates building base materials for dumping.
+function undump_buildings()
+    local buildings = df.global.world.buildings.all
+    local undumped = 0
+    for i = 0, #buildings - 1 do
+        local building = buildings[i]
+        -- Zones and stockpiles don't have the contained_items field.
+        if not (df.building_civzonest:is_instance(building) or
+            df.building_stockpilest:is_instance(building)) then
+            local items = building.contained_items
+            for j = 0, #items - 1 do
+                local contained = items[j]
+                if contained.use_mode == 2 and contained.item.flags.dump then
+                    -- print(building, contained.item)
+                    undumped = undumped + 1
+                    contained.item.flags.dump = false
+                end
+            end
+        end
+    end
+    
+    if undumped > 0 then
+        local s = "s"
+        if undumped == 1 then s = "" end
+        print("Undumped "..undumped.." item"..s..".")
+    end
+end
+
+undump_buildings()