Add an error code for a transaction that violates invariants.

src/cpp/ripple/TransactionEngine.cpp

@@ -160,6 +160,7 @@ TER TransactionEngine::applyTransaction(const SerializedTransaction& txn, Transa
 				cLog(lsFATAL) << transToken(terResult) << ": " << transHuman(terResult);
 				cLog(lsFATAL) << mNodes.getJson(0);
 				didApply = false;
+				terResult = tefINTERNAL;
 			}
 			else
 			{

src/cpp/ripple/TransactionErr.cpp

@@ -38,6 +38,7 @@ bool transResultInfo(TER terCode, std::string& strToken, std::string& strHuman)
 		{	tefGEN_IN_USE,			"tefGEN_IN_USE",			"Generator already in use."								},
 		{	tefNO_AUTH_REQUIRED,	"tefNO_AUTH_REQUIRED",		"Auth is not required."									},
 		{	tefPAST_SEQ,			"tefPAST_SEQ",				"This sequence number has already past."				},
+		{	tefINTERNAL,			"tefINTERNAL",				"Internal error."										},
 
 		{	telLOCAL_ERROR,			"telLOCAL_ERROR",			"Local failure."										},
 		{	telBAD_DOMAIN,			"telBAD_DOMAIN",			"Domain too long."										},

src/cpp/ripple/TransactionErr.h

@@ -81,6 +81,7 @@ enum TER	// aka TransactionEngineResult
 	tefGEN_IN_USE,
 	tefNO_AUTH_REQUIRED,	// Can't set auth if auth is not required.
 	tefPAST_SEQ,
+	tefINTERNAL,
 
 	// -99 .. -1: R Retry (sequence too high, no funds for txn fee, originating account non-existent)
 	// Causes: