Replace print()s with minetest.log() in builtin

builtin/chatcommands.lua

@@ -471,10 +471,10 @@ minetest.register_chatcommand("spawnentity", {
 			minetest.chat_send_player(name, "entityname required")
 			return
 		end
-		print('/spawnentity invoked, entityname="'..entityname..'"')
+		minetest.log("action", '/spawnentity invoked, entityname="'..entityname..'"')
 		local player = minetest.get_player_by_name(name)
 		if player == nil then
-			print("Unable to spawn entity, player is nil")
+			minetest.log("error", "Unable to spawn entity, player is nil")
 			return true -- Handled chat message
 		end
 		local p = player:getpos()
@@ -491,7 +491,7 @@ minetest.register_chatcommand("pulverize", {
 	func = function(name, param)
 		local player = minetest.get_player_by_name(name)
 		if player == nil then
-			print("Unable to pulverize, player is nil")
+			minetest.log("error", "Unable to pulverize, player is nil")
 			return true -- Handled chat message
 		end
 		if player:get_wielded_item():is_empty() then

builtin/modmgr.lua

@@ -778,7 +778,7 @@ function modmgr.handle_configure_world_buttons(fields)
 		end
 
 		if not worldfile:write() then
-			print("failed to write world config file")
+			minetest.log("error", "Failed to write world config file")
 		end
 
 		modmgr.modlist = nil
@@ -932,7 +932,7 @@ function modmgr.preparemodlist(data)
 			if element ~= nil then
 				element.enabled = engine.is_yes(value)
 			else
-				print("Mod: " .. key .. " " .. dump(value) .. " but not found")
+				minetest.log("info", "Mod: " .. key .. " " .. dump(value) .. " but not found")
 			end
 		end
 	end

builtin/serialize.lua

@@ -178,7 +178,7 @@ function minetest.deserialize(sdata)
 	if okay then
 		return results
 	end
-	print('error:'.. results)
+	minetest.log('error', 'minetest.deserialize(): '.. results)
 	return nil
 end