sign_for RPC command (RIPD-182):

The sign_for RPC command returns a field suitable for
signing a multi-signed transaction.  Actual multi-signed
transactions are in the next commit.

src/ripple/overlay/impl/PeerImp.cpp

@@ -1652,7 +1652,8 @@ PeerImp::checkTransaction (Job&, int flags,
         }
 
         bool const trusted (flags & SF_TRUSTED);
-        getApp().getOPs ().processTransaction (tx, trusted, false, false);
+        getApp().getOPs ().processTransaction (
+            tx, trusted, false, NetworkOPs::FailHard::no);
     }
     catch (...)
     {