Use src/lib/w32/w32sockets.c for client

Move client's w32_connect() to w32sockets.c.

Replace w32_recv() and w32_send() by read() and write().

Replace w32_close() by w32_close_function.

Replace call of WSAStartup() in w32_sysdep_init() by
w32_socket_init().

Remove the identical copies of fd_is_socket(),
w32_set_winsock_errno(), w32_socket().

src/client/expect.c

@@ -39,23 +39,12 @@
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
-#ifdef _WIN32
-#include "w32types.h"
-#else
 #include <sys/types.h>
 #include <sys/socket.h>
 #include <unistd.h>
-#endif
 #include "misc.h"
 #include "proto.h"
 
-#ifdef _WIN32
-#define read(sock, buffer, buf_size) \
-	w32_recv((sock), (buffer), (buf_size), 0)
-#define write(sock, buffer, buf_size) \
-	w32_send((sock), (buffer), (buf_size), 0)
-#endif
-
 int
 recvline(int s, char *buf)
 {