Do a better job on Connection: header processing in client requests.

Do a better job on Connection: header processing in client requests.

Add a flag field for each HTTP header and define a bit HDF_FILTER
to mean "filter this out", and initialize to zero all relevant
places.

If HDF_FILTER is set, do not copy the header across when filtering.

Run through Connection: header (if present) and set HDF_FILTER on
any header that matches a word in the contents.

If we are not HTTP/1.1 and have no Connection header, we close
the session when this reqest is done.

If we have a Connection header, we respect that.

git-svn-id: svn+ssh://projects.linpro.no/svn/varnish/trunk@832 d4fa192b-c00b-0410-8231-f00ffab90ce4