re-allow point updating with reorder buffer

[Dieterbe]

We need to revise #1201

There is a legitimate use case for wanting to overwrite the last point. we have a customer who has points that are composed of aggregates of jobs, and they can't predict the number of jobs or when they'll complete, so the most practical and useful thing is to send a point (and update if necessary) each time a new value comes in

Awoods suggested adding a config flag to control whether MT should use the first or last value.

[replay]

just for clarification, with the rob it used to be possible to update any datapoint in the rob, not only the last one. we will need to have that same behavior again.

[Dieterbe]

this is now high priority.