Error return for server too busy.

src/cpp/ripple/RPCErr.cpp

@@ -71,6 +71,7 @@ Json::Value rpcError(int iError, Json::Value jvResult)
 		{ rpcTXN_NOT_FOUND,			"txnNotFound",		"Transaction not found."								},
 		{ rpcUNKNOWN_COMMAND,		"unknownCmd",		"Unknown method."										},
 		{ rpcWRONG_SEED,			"wrongSeed",		"The regular key does not point as the master key."		},
+		{ rpcTOO_BUSY,				"tooBusy",			"The server is too busy to help you now."               },
 	};
 
 	int		i;

src/cpp/ripple/RPCErr.h

@@ -17,6 +17,7 @@ enum {
 	rpcNO_PERMISSION,
 	rpcNO_EVENTS,
 	rpcNOT_STANDALONE,
+	rpcTOO_BUSY,
 
 	// Networking
 	rpcNO_CLOSED,