Merge branch 'http-connect'

After this patchset http-connect works with pproxy [1]:

    $ pproxy -l http://:8000/ -vvv &
    $ http-connect //127.1:8000 http://kernel.org:80/

  [1]: https://pypi.org/project/pproxy/

* http-connect:
  http-connect: do not check connection on GET cb
  http-connect: set Host header (for CONNECT and GET) (like curl)
  http-connect: cleanup and helpers
  http: do not close connection for CONNECT
  http: do not assume body for CONNECT

Fixes: #946