Generated .pyi files reference 'long', which is not Python 3 compatible

[gvanrossum]

I can think of two ways to fix this:

1. The easy way: replace 'long' with 'int' here
2. Do something with the override_dict

A potential problem for (1) would be that it will not only change the generated .pyi files but also the generated .py files. I do think that even in Python 2 the distinction between int and long is rarely useful though, so perhaps this is acceptable.

The problem with (2) is that it's a lot more code, since the architecture for the override_dict doesn't really map cleanly to the way is_integer_type() is used. (In order to allow separate mappings for Int32, UIint32, Int64 and UInt64, we'd need 4 isinstance checks.)