testbench.py: add an option to disable (just) the in-memory cache
dwiki-cat.py: use an IP address for REMOTE_ADDR, not a hostname

Various downstream things now care that REMOTE_ADDR is a real IP address
instead of just, you know, random stuff.
Provide a way to manually force things into the brute force cache

This adds a new command and some trivial support infrastructure in the
code to force always caching (if the 'response' is cacheable).
Slightly improve security for cookies and in responses

We now try to set various modern HTTP flags to make cookies and our
pages more 'secure'. This is mostly superstitious hand-waving but
what the heck.
Use greater-than If-Modified-Since comparison for Tiny Tiny RSS

As a very special hack, change If-Modified-Since processing logic to use
a greater-than check instead of a strictly-equal-to check for requests
from Tiny Tiny RSS because otherwise TTR will never ever do a successful
conditional GET.

See http://utcc.utoronto.ca/~cks/space/blog/web/IfModifiedSinceHowNot
for a long discussion (with links) about this issue and TTR mishandling.
Add more control over what Atom feeds get forced into the BFC when

- bfc-atom-nocond-ttl no longer implies that the request is forced into
  the cache; you can/have to set that separately. (Well, the request's
  reply if it's cacheable.)
- you can force all Atom requests into the cache if desired.