Ideally, the log would go in the exception's ctor, but
two log levels are used, so I'd need to specify the level
in the ctor, which isn't great as it's not really related
to the exception.
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.
