NUVIE: Improve cursor responsiveness of main menu

Still need to re-generate the ultima.dat to include it,
once I'm sure nothing else needs to be change prior to
the next release

devtools/create_ultima/files/ultima6/scripts/u6/intro.lua

@@ -3052,6 +3052,7 @@ local function main_menu()
 	g_menu["title"].visible = true
 	g_menu["subtitle"].visible = true
 	g_menu["menu"].visible = true
+	canvas_set_update_interval(10)
 
 	local input
 
@@ -3064,6 +3065,8 @@ local function main_menu()
 		end
 
 		if input ~= nil then
+			canvas_set_update_interval(25)
+
 			if input == 113 then     --q quit
 				return "Q"
 			elseif input == 105 or input == 13 and g_menu_idx == 0 then --i
@@ -3157,7 +3160,9 @@ local function main_menu()
 					end
 				end
 			end
+
 			input = nil
+			canvas_set_update_interval(10)
 		end
 	end
 end