- 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.