this could cause invalid paths to be returned for AF_UNIX sockets on some
platforms (including FreeBSD 4.2-RELEASE), appearantly because there is
no assurance that the address will be nul-terminated when filled in by the
kernel.

PySocketSock_recvfrom():  Use PyString_AS_STRING() to get the data pointer
    of a string we create ourselves; there is no need for the extra type
    check from PyString_AsString().

This closes SF bug #416573.