[brisbane-core/MERGE] Use hash(key) for internal node lookups

[John Arbash Meinel]

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Attached is my update to the brisbane-core CHKMap code to support
hash(key) as the "search_key" rather than using the raw key itself.

It is parameterized, so we still support plain "--development4", as well
as a new '--development4-hash16' and '--development4-hash255'. This
gives us a couple easy-to-tweak knobs as we evaluate performance,
latency tradeoffs, etc.

(I also updated the repository-details plugin to understand the new
formats.)

I'm pretty confident about landing these, and also pretty confident that
we want some form of hash-prefix in the final form. (I even made sure
that hash collisions won't cause infinite recursion as it tries to split
the leaf nodes.)

John
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