Make winsock.h and winsock2.h independent from the Unix headers.
Make them compatible with both the Unix C headers and the MSVCRT
headers.
Ensure compatibility with the Unix headers via the USE_WS_PREFIX
macro.
Add WINE_NOWINSOCK: prevents winsock.h from being included from
windows.h when defined.
Add ws2tcpip.h, move definitions to the right header.

diff --git a/include/windows.h b/include/windows.h
index 595294f..a041926 100644
--- a/include/windows.h
+++ b/include/windows.h
@@ -35,8 +35,10 @@
 #include "shellapi.h"
 /* #include "winperf.h" */
 
+#ifndef WINE_NOWINSOCK
 #include "winsock2.h"
 /* #include "mswsock.h" */
+#endif /* WINE_NOWINSOCK */
 
 #ifndef NOCRYPT
 #include "wincrypt.h"