set_socketpair_eids.
* fhandler_socket.cc (fhandler_socket::set_socketpair_eids): New method.
(fhandler_socket::dup): Duplicate sec_pipe if necessary.
(fhandler_socket::listen): Only create sec_pipe if named pipes are
available. Initialized sec_peer_pid to 0 as on Linux.
(fhandler_socket::connect): Only run eid credential transaction if
named pipes are available. Fake otherwise. Initialized sec_peer_pid
to 0 as on Linux.
(fhandler_socket::accept): Ditto.
(fhandler_socket::close): Move closing sec_pipe handle from here...
(fhandler_socket::~fhandler_socket): ... to here.
* net.cc (socketpair): Set eid credentials by calling
fhandler_socket::set_socketpair_eids() on both socket ends.
* wincap.h (wincaps::has_named_pipes): New element.
* wincap.cc: Implement above element throughout.