osutil: use PyLongObject in recvfds
PyIntObject doesn't exist in Python 3. While PyIntObject is preferred
on Python 2 because it is a fixed capacity and faster, the difference
between PyIntObject and PyLongObject for scenarios where performance
isn't critical or the caller isn't performing type checking shouldn't
be relevant.
So change recvfds to return a list of longs instead of ints on Python
2.