Use src/lib/w32/w32io.c for client

Replaces w32_writev_socket() and w32_readv_fd().  Split w32types.h off
w32misc.h, to avoid putting irrelevant stuff into client tarball.

src/client/expect.c

@@ -39,7 +39,9 @@
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
-#ifndef _WIN32
+#ifdef _WIN32
+#include "w32types.h"
+#else
 #include <sys/types.h>
 #include <sys/socket.h>
 #include <unistd.h>