Implemented overlapped WSARecvFrom(), WSASendTo(), and
WSAGetOverlappedResult().
Fixed shutdown() to work correctly for overlapped sockets (do not
actually do a shutdown() system call as long as there are pending
overlapped requests).
Also added correct error reporting when trying to read or write on a
shut down connection, also for ReadFile()/WriteFile() calls.

diff --git a/include/winbase.h b/include/winbase.h
index 73620ce..ba3785e 100644
--- a/include/winbase.h
+++ b/include/winbase.h
@@ -458,7 +458,7 @@
 
 /* The 'overlapped' data structure used by async I/O functions.
  */
-typedef struct {
+typedef struct _OVERLAPPED {
         DWORD Internal;
         DWORD InternalHigh;
         DWORD Offset;