Random fixes to hippotat

[Mark Wooding]

I now have this installed and running.  I had to fix it; my fixes are in

        https://git.distorted.org.uk/~mdw/hippotat/

in the branch

        mdw/fixes      e13eca8e1facf849a7825b815adc72ef142b7ca8

I've done some archaeology on the spurious-`Content-Length' bug, and I
can't see any reason why anything written even slightly recently would
try to set `Content-Length' explicitly.

I also have fixes for `userv-utils', which I shall write about
separately.

-- [mdw]