late-bind my App.* handlers

This came up when trying to integrate my apps with the vudu debugger
(https://github.com/deltadaedalus/vudu). In general, it's a subtle part
of LÖVE's semantics that you can modify event handlers any time and your
modifications will get picked up. Now my Freewheeling Apps will follow
this norm as well.

app.lua

@@ -406,6 +406,7 @@ local Keys_down = {}
 -- can't run any tests after this
 function App.disable_tests()
   -- have LÖVE delegate all handlers to App if they exist
+  -- make sure to late-bind handlers like LÖVE's defaults do
   for name in pairs(love.handlers) do
     if App[name] then
       -- love.keyboard.isDown doesn't work on Android, so emulate it using
@@ -421,7 +422,7 @@ function App.disable_tests()
                                 return App.keyreleased(key, scancode)
                               end
       else
-        love.handlers[name] = App[name]
+        love.handlers[name] = function(...) App[name](...) end
       end
     end
   end