my app heavily depends on STI and without this patch my dashboard
takes > 3000ms with the patch applies < 300ms (still too slow, I
know). As i'm just adding "memoize :find_sti_class" to AR::Base I
believe the patch should be safe - but maybe I'm wrong as this will
reference the class constants and the class unloading in dev-mode
Also I have not written a test as I'm not too sure what to test - If
you come up with a clever way of testing this let me know and I'll
write that test!