Still needs testing (and need to write a few more unit tests), but
everything should be there. Lots of unfortunate duplication,
but...well, I can't see a way around it using LMDB.
A couple of other minor changes in this commit, only slightly relevant.
tried rebasing, tree-filter, and many other things. at this point,
the history of these files previous to this can live on
in my bc2 branch, as I'm importing them as-is to here.
