Fire the individual original callbacks when using transactions

Fixes #1089

lib/multi.js

@@ -36,6 +36,7 @@ function pipeline_transaction_command (self, command_obj, index) {
         // Keep track of who wants buffer responses:
         // By the time the callback is called the command_obj got the buffer_args attribute attached
         self.wants_buffers[index] = command_obj.buffer_args;
+        command_obj.callback = tmp;
     };
     self._client.internal_send_command(command_obj);
 }