Windows: Use Standard Networking Functions If Possible

Currently, the Windows code use Winsock2-specific APIs to try to emulate
calls such as inet_pton(), inet_ntop() and if_nametoindex(), which may not
do the job all the time.  On Vista and later, Winsock2 does provide a
proper implementation for these functions, so we can use them if they exist
on the system, by querying for them during g_networking_init().  Otherwise,
we continue to use the original code path for these, in the case of XP and
Server 2003.

This enables many of the network-address tests to pass on Windows as a
result, when the native Winsock2 implementations can be used.

https://bugzilla.gnome.org/show_bug.cgi?id=730352

gio/gnetworking.c

@@ -22,6 +22,13 @@
 
 #include "gnetworking.h"
 
+#ifdef G_OS_WIN32
+/* For Windows XP run-time compatibility */
+#include "gwin32networking.h"
+
+GWin32WinsockFuncs ws2funcs = {0};
+#endif
+
 /**
  * SECTION:gnetworking
  * @title: gnetworking.h
@@ -66,9 +73,39 @@ g_networking_init (void)
   if (g_once_init_enter (&inited))
     {
       WSADATA wsadata;
+      HMODULE ws2dll, iphlpapidll;
 
       if (WSAStartup (MAKEWORD (2, 0), &wsadata) != 0)
-	g_error ("Windows Sockets could not be initialized");
+        g_error ("Windows Sockets could not be initialized");
+
+      /* We want to use these functions if they are available, but
+       * still need to make sure the code still runs on Windows XP
+       */
+      ws2dll = LoadLibraryW (L"ws2_32.dll");
+      iphlpapidll = LoadLibraryW (L"iphlpapi.dll");
+
+      if (ws2dll != NULL)
+        {
+          ws2funcs.pInetNtop =
+            (PFN_InetNtop) GetProcAddress (ws2dll, "inet_ntop");
+          ws2funcs.pInetPton =
+            (PFN_InetPton) GetProcAddress (ws2dll, "inet_pton");
+          FreeLibrary (ws2dll);
+        }
+      else
+        {
+          ws2funcs.pInetNtop = NULL;
+          ws2funcs.pInetPton = NULL;
+        }
+
+      if (iphlpapidll != NULL)
+        {
+          ws2funcs.pIfNameToIndex =
+            (PFN_IfNameToIndex) GetProcAddress (iphlpapidll, "if_nametoindex");
+          FreeLibrary (iphlpapidll);
+        }
+      else
+        ws2funcs.pIfNameToIndex = NULL;
       
       g_once_init_leave (&inited, 1);
     }