[Twisted-Python] twisted.lumberjack clobbers existing logs

Hi everyone... I like the twisted.lumberjack module that was recently added, but I think it has a small buglet. It checks the size of the existing log file, but then opens it in mode "w", truncating it. Thus, I suggest the last line of LogFile._openFile should change from: self._file = open(self.path, "w") to: self._file = open(self.path, "a") -Andrew.