[DGD] Kotaka improvements

[Shentino]

After wrangling for hours with LIB_CONN and LIB_USER, I finally
managed to implement mandatory connection filtering that even handles
the redirect-within-querytimeout trick that ~Game uses to get instant
I/O and avoid the "show a banner and then twiddle thumbs waiting for
more input" routine.

As a demonstration, now all connections that come in are stacked up
with a couple of useful filters.  First, the rlimits filter which
wraps all user I/O inside a call_limited, and atomic which makes all
I/O tasks atomic.

Comments appreciated.

I feel kind of wicked though, this is rather a man in the middle
attack where the "attacker" has sovereign immunity from being System.

As always, latest work is on my github repo under the kotaka module.