This patch fixes possible overflows in the socket module for 64-bit
platforms (mainly Win64). The changes are:

- abstract the socket type to SOCKET_T (this is SOCKET on Windows, int
on Un*x), this is necessary because sizeof(SOCKET) > sizeof(int) on
Win64

- use INVALID_SOCKET on Win32/64 for an error return value for
accept()

- ensure no overflow of the socket variable for: (1) a PyObject return
value (use PyLong_FromLongLong if necessary); and (2) printf
formatting in repr().

Closes SourceForge patch #100516.