[MERGE] Review feedback on hash trie inventories, and describe radix tree inventories, plus some details on hash trie implementation.

[John Arbash Meinel]

John Arbash Meinel has voted tweak.
Status is now: Conditionally approved
Comment:
just making sure vila's tweak vote is reflected in BB

For details, see: 
http://bundlebuggy.aaronbentley.com/project/bzr/request/%3C1219798121.31549.383.camel%40lifeless-64%3E
Project: Bazaar