- Use 'Pair' again, but this time, the key is an int64 that the selected sort field will be casted to.
We therefore have now only one type of sort.
- Check validity of sort string early on.
- Ensure that the ConnInfo's field used by the sort is not the value from 'client', but really the one
that was used for the sort.
- Added a test for sort by Idle time.
- fix bug that did not update last activity on message delivery
- added sort capabilities for last activity
- avoid extra Reverse by simply changing Less func