bandwidth limiting

[Brian Warner]

It would be awfully handy if an application could tell Foolscap to limit the outgoing bandwidth it is using to some N bits per second. It would also be useful to have it limit the inbound bandwidth, but of course that's a lot harder.

This needs to be done on at least the Tub level. If an app has multiple Tubs, it would be nice if they could coordinate to keep their aggregate limit below the configured value. (it would even be cool if the bandwidth manager were a foolscap.Referenceable object, so it could be shared between multiple applications, perhaps on different hosts, all sharing the same narrow pipe).