Python3: Fix doctest for _callable_description
Python3: Fix doctest for _callable_description

On Python 2, our `from builtins import *` replaces `int`, so
`int.__name__` is actually "newint" not "int".

`eval` is the same on Python 2 & 3 so I'm using that instead. The
intention of the test here is to test that we handle
`functools.partial`, nothing specific to `int` itself.

stb-tester/stb-tester,stb-tester/stb-tester,stb-tester/stb-tester,stb-tester/stb-tester