Make circuit isolation isolate exits? (signal NEWNYM exit bucketing)

Would like to see an option for bucketing exits on NEWNYM such that dynamic maps thrown out by NEWNYM will have their exits bucketed and quarantined from further use until all other exit's have been bucketed by NEWNYM. At which point further NEWNYM's or circuit requests round robin exits out of the bucket for such use.

Reason: Exits seem to be reused sometime after NEWNYM, guaranteed robin on NEWNYM makes some cases of testing tor and destinations easier.

Integration: rendevous, other limitations on exits (country), static maps, etc.