fixed compile errors when using old version of jsonrpcstub, fixed #1003

cmake/scripts/jsonrpcstub.cmake

@@ -28,9 +28,18 @@ execute_process(
 	COMMAND ${ETH_JSON_RPC_STUB} ${ETH_SPEC_PATH} 
 		--cpp-server=${ETH_SERVER_NAME} --cpp-server-file=${SERVER_TMPFILE}
 		--cpp-client=${ETH_CLIENT_NAME} --cpp-client-file=${CLIENT_TMPFILE} 
+		OUTPUT_VARIABLE ERR ERROR_QUIET
 )
 
-include("${ETH_SOURCE_DIR}/cmake/EthUtils.cmake")
-replace_if_different("${SERVER_TMPFILE}" "${SERVER_OUTFILE}")
-replace_if_different("${CLIENT_TMPFILE}" "${CLIENT_OUTFILE}")
+# don't throw fatal error on jsonrpcstub error, someone might have old version of jsonrpcstub,
+# he does not need to upgrade it if he is not working on JSON RPC
+# show him warning instead
+if (ERR)
+	message(WARNING "Your version of jsonrcpstub tool is not supported. Please upgrade it.")
+	message(WARNING "${ERR}")
+else()
+	include("${ETH_SOURCE_DIR}/cmake/EthUtils.cmake")
+	replace_if_different("${SERVER_TMPFILE}" "${SERVER_OUTFILE}")
+	replace_if_different("${CLIENT_TMPFILE}" "${CLIENT_OUTFILE}")
+endif()