server should black-list faulty clients
Imported issue: Initially reported by @zimmerma in https://gforge.inria.fr/tracker/?group_id=2065&aid=21814
when a client sends say more than 3 consecutive failing workunits, the server should black-list that client. Indeed, with very high probability further workunits will fail on that client. This will both increase load on the server, and workunits will not be resubmitted after maxwuerror tries, thus the corresponding workunits will be lost.