More preparatory work: remove the <windows.h> include from lots of

source files in which it's no longer required (it was previously
required in anything that included <putty.h>, but not any more).
Also moved a couple of stray bits of exposed WinSock back into
winnet.c (getservbyname from ssh.c and AF_INET from proxy.c).

[originally from svn r2160]

x11fwd.c

@@ -1,4 +1,3 @@
-#include <windows.h>
 #include <stdio.h>
 #include <stdlib.h>