If a facet, during X, asserts X, for all X, then X includes all
`Observe` assertions. Assertion of X should be a no-op (though
subsequent retractions of X will have no effect!) since duplicates are
ignored. However, the implementation had been ignoring whether it had
seen `Observe` assertions before, and was *always* (re)placing them
into the index, leading to runaway growth.
The repair is to only process `Observe` records on first assertion and
last retraction.
As part of this change, Dataspaces have been given names, and some
cruft from the previous implementation has been removed.
Tony Garnock-Jones
2b296d79c7