Get ext. IP from UPnP, make sure addrMe IsRoutable() in version.

This fixes a potential bug where some NATs may replace the node's
interal IP with its external IP in version messages, causing
incorrect checksums when version messages begin being checksummed
on February 14, 2012.

src/net.cpp

@@ -1103,6 +1103,26 @@ void ThreadMapPort2(void* parg)
     r = UPNP_GetValidIGD(devlist, &urls, &data, lanaddr, sizeof(lanaddr));
     if (r == 1)
     {
+        if (!addrLocalHost.IsRoutable())
+        {
+            char externalIPAddress[40];
+            r = UPNP_GetExternalIPAddress(urls.controlURL, data.first.servicetype, externalIPAddress);
+            if(r != UPNPCOMMAND_SUCCESS)
+                printf("UPnP: GetExternalIPAddress() returned %d\n", r);
+            else
+            {
+                if(externalIPAddress[0])
+                {
+                    printf("UPnP: ExternalIPAddress = %s\n", externalIPAddress);
+                    CAddress addrExternalFromUPnP(externalIPAddress, 0, false, nLocalServices);
+                    if (addrExternalFromUPnP.IsRoutable())
+                        addrLocalHost = addrExternalFromUPnP;
+                }
+                else
+                    printf("UPnP: GetExternalIPAddress failed.\n");
+            }
+        }
+
         string strDesc = "Bitcoin " + FormatFullVersion();
 #ifndef UPNPDISCOVER_SUCCESS
         /* miniupnpc 1.5 */