Don't sign a transaction for non-admin when under load.

src/cpp/ripple/RPCHandler.cpp

@@ -60,6 +60,9 @@ RPCHandler::RPCHandler (NetworkOPs* netOps, InfoSub::pointer infoSub) : mNetOps
 
 Json::Value RPCHandler::transactionSign (Json::Value params, bool bSubmit, bool bFailHard, ScopedLock& mlh)
 {
+    if (getApp().getFeeTrack().isLoaded() && (mRole != ADMIN))
+        return rpcError(rpcTOO_BUSY);
+
     Json::Value     jvResult;
     RippleAddress   naSeed;
     RippleAddress   raSrcAddressID;