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/play.c

@@ -45,6 +45,7 @@
 #else
 #include <process.h>
 #include <io.h>
+#include "w32types.h"
 #endif
 #include "linebuf.h"
 #include "misc.h"