* src/assuan-pipe-connect.c (initial_handshake): Get peer's PID
from the initial interaction.
* src/assuan-pipe-server.c (assuan_init_pipe_server): Handle the case
of FILEDES == NULL on Windows.
* tests/Makefile.am [HAVE_W32_SYSTEM] (TESTS): Add fdpassing.
* tests/fdpassing.c: Remove including sys/socket.h and sys/wait.h.
(cmd_echo): Output to stder, as stdout is /dev/null.
(main): Support Windows.