Did some more exploration and perf tuning and thinking on caching
databases, and am pretty sure I know how I want to implement it. Will be
several stages, starting with using it for generating views, and ending(?)
with using it for direct mode file mappings.

Not sure I'm ready to dive into that yet, so instead spent the rest of the
day working on small bugfixes and improvements. Only two significant ones..

Made the webapp use a constant time string comparison (from `securemem`)
to check if its auth token is valid. This could help avoid a potential
timing attack to guess the auth token, although that is theoretical.
Just best practice to do this.

Seems that openssh 6.5p1 had another hidden surprise (in addition to
its now-fixed bug in handing hostnames in `.ssh/config`) -- it broke
the method git-annex was using for stopping a cached ssh connection,
which led to some timeouts for failing DNS lookups. If git-annex seems
to stall for a few seconds at startup/shutdown, that may be why
(--debug will say for sure). I seem to have found a workaround that
avoids this problem.
