Thanks Hos for taking care of this.
I have to clarify two things:
1. I changed the wrong property when creating the patch , the only thing I should have changed was as I said in the description:
2. the reason filename was not changed, is that according to http://stackoverflow.com/questions/11527194/jetty-access-log-is-no-longer-logging is not clear filename must match filenameDateFormat, and that retainDays won't work if you change that format (see Bob Kuhar's comment). And I have verified the filename created is correct when changing just filenameDateFormat
so not sure you should change filename, up to you.