Allow interaction with nodes while wielding these items.

- beds
- boats
- carts
- key/skeleton key
- seeds

All these had on_place handlers that did not allow nodes with
an on_rightclick() handler to be used first (if not using
sneak). This code is taken from the torches mod and applied
everywhere.

This allows all these items to e.g. be inserted into the `frame`
mod's item frames.

mods/farming/api.lua

@@ -313,6 +313,15 @@ farming.register_plant = function(name, def)
 		}),
 
 		on_place = function(itemstack, placer, pointed_thing)
+			local under = pointed_thing.under
+			local node = minetest.get_node(under)
+			local udef = minetest.registered_nodes[node.name]
+			if udef and udef.on_rightclick and
+					not (placer and placer:get_player_control().sneak) then
+				return udef.on_rightclick(under, node, placer, itemstack,
+					pointed_thing) or itemstack
+			end
+
 			return farming.place_seed(itemstack, placer, pointed_thing, mname .. ":seed_" .. pname)
 		end,
 		next_plant = mname .. ":" .. pname .. "_1",