storage slabs.  Pretty soon we will not be doing that directly and
we want only one place to know about the gzip/gunzip magic.

Overhaul the chunked encoding fetcher code, to be much simpler and 
much more robust.

Sort out some 4GB issues while we where here anyway.



git-svn-id: http://www.varnish-cache.org/svn/trunk/varnish-cache@5702 d4fa192b-c00b-0410-8231-f00ffab90ce4