Support "standalone" mode (-a or --standalone) in which we do not connect

to the network and do not close ledgers. This mode makes it much easier to
test transactions as they are only applied once to the open ledger.

src/RPCServer.cpp

@@ -832,6 +832,9 @@ Json::Value RPCServer::doAccountWalletSet(const Json::Value& params) {
 
 Json::Value RPCServer::doConnect(const Json::Value& params)
 {
+	if (theConfig.RUN_STANDALONE)
+		return "cannot connect in standalone mode";
+
 	// connect <ip> [port]
 	std::string strIp;
 	int			iPort	= -1;