Move the vcl_fetch{} execution up between fetching the headers and the
body of the backend response.

This makes obj.* unavailable in vcl_fetch{} and replaces it with a
new beresp.* family of variables.

This paves the way for a lot of good stuff, such as streaming pass,
on-the-fly delivery of misses, storage selection based on headers
etc.



git-svn-id: http://www.varnish-cache.org/svn/trunk@3838 d4fa192b-c00b-0410-8231-f00ffab90ce4