This PR fixes small issues that I noticed while implementing proposal validation and fixing some external join bugs:
The pseudocode for determining whether a path is required assumes that all proposals are by-reference. The PR updates the pseudocode to be more general, and also account for proposals by value.
There were two references to adding a single leaf to the tree, which are updated to make clear that the tree grows by doubling, not by single leaves.
There was no current requirement that an Update proposal have a distinct encryption_key, so one is added.
This PR fixes small issues that I noticed while implementing proposal validation and fixing some external join bugs:
encryption_key, so one is added.