Added -externalip and -discover

-externalip=<ip> can be used to explicitly set the public IP address
of your node. -discover=0 can be used to disable the automatic public
IP discovery system.

src/net.h

@@ -49,6 +49,9 @@ enum
     LOCAL_UPNP,
     LOCAL_IRC,
     LOCAL_HTTP,
+    LOCAL_MANUAL,
+
+    LOCAL_MAX
 };
 
 bool AddLocal(const CNetAddr& addr, int nScore = LOCAL_NONE);