* Retire pending deletions at start of plan
Instead of letting pending deletions pile up to be retired at the end of
a plan, this commit eagerly disposes of any pending deletions that were
pending at the end of the previous plan. This is a nice usability win
and also reclaims an invariant that at most one resource with a given
URN is live and at most one is pending deletion at any point in time.
* Rebase against master
* Fix a test issue arising from shared snapshots
* CR feedback
* plan -> replacement
* Use ephemeral statuses to communicate deletions
* Work around a potentially bad assert in the engine
The engine asserts if presented with a plan that deletes the same URN
more than once. This has been empirically proven to be possible, so I am
removing the assert.
* CR: Add log for multiple pending-delete deletes
