[libmicrohttpd] MHD_USE_DUAL_STACK and Windows

[Luke-Jr]

MHD_USE_DUAL_STACK in libmicrohttpd currently just *inhibits setting* the 
IPV6_V6ONLY socket option, but per Microsoft's documentation 
http://msdn.microsoft.com/en-us/library/windows/desktop/bb513665(v=vs.85).aspx
the default on Windows is that this is enabled, thus MHD_USE_DUAL_STACK will 
not work (since it leaves the default). libmicrohttpd should probably just 
unconditionally set IPV6_V6ONLY to the desired value when the option is 
available.

diff --git a/src/microhttpd/daemon.c b/src/microhttpd/daemon.c
index 0a33b77..3cbf28e 100644
--- a/src/microhttpd/daemon.c
+++ b/src/microhttpd/daemon.c
@@ -3493,8 +3493,7 @@ MHD_start_daemon_va (unsigned int flags,
        }
       daemon->socket_fd = socket_fd;
 
-      if ( (0 != (flags & MHD_USE_IPv6)) &&
-          (MHD_USE_DUAL_STACK != (flags & MHD_USE_DUAL_STACK)) )
+      if (0 != (flags & MHD_USE_IPv6))
        {
 #ifdef IPPROTO_IPV6
 #ifdef IPV6_V6ONLY
@@ -3503,10 +3502,11 @@ MHD_start_daemon_va (unsigned int flags,
             and may also be missing on older POSIX systems; good luck if you 
have 
any of those,
             your IPv6 socket may then also bind against IPv4 anyway... */
 #ifndef WINDOWS
-         const int on = 1;
+         const int
 #else
-         const char on = 1;
+         const char
 #endif
+                on = (MHD_USE_DUAL_STACK != (flags & MHD_USE_DUAL_STACK));
          if ( (0 > SETSOCKOPT (socket_fd,
                                IPPROTO_IPV6, IPV6_V6ONLY,
                                &on, sizeof (on))) &&