TicketSequence with non-zero Sequence is an error:

Before this change any non-zero Sequence field was handled as
a non-ticketed transaction, even if a TicketSequence was
present.  We learned that this could lead to user confusion.
So the rules are tightened up.

Now if any transaction contains both a non-zero Sequence
field and a TicketSequence field then that transaction
returns a temSEQ_AND_TICKET error code.

The (deprecated) "sign" and "submit" RPC commands are tuned
up so they auto-insert a Sequence field of zero if they see
a TicketSequence in the transaction.

No amendment is needed because this change is going into
the first release that supports the TicketBatch amendment.

src/ripple/protocol/TER.h

@@ -115,9 +115,10 @@ enum TEMcodes : TERUnderlyingType {
     temCANNOT_PREAUTH_SELF,
     temINVALID_COUNT,
 
-    // An intermediate result used internally, should never be returned.
-    temUNCERTAIN,
-    temUNKNOWN,
+    temUNCERTAIN,  // An internal intermediate result; should never be returned.
+    temUNKNOWN,    // An internal intermediate result; should never be returned.
+
+    temSEQ_AND_TICKET,
 };
 
 //------------------------------------------------------------------------------

src/ripple/protocol/impl/TER.cpp

@@ -152,6 +152,7 @@ transResults()
         MAKE_ERROR(temINVALID_ACCOUNT_ID,     "Malformed: A field contains an invalid account ID."),
         MAKE_ERROR(temCANNOT_PREAUTH_SELF,    "Malformed: An account may not preauthorize itself."),
         MAKE_ERROR(temINVALID_COUNT,          "Malformed: Count field outside valid range."),
+        MAKE_ERROR(temSEQ_AND_TICKET,         "Transaction contains a TicketSequence and a non-zero Sequence."),
 
         MAKE_ERROR(terRETRY,                  "Retry transaction."),
         MAKE_ERROR(terFUNDS_SPENT,            "DEPRECATED."),