The delivered document's age should be computed relative to the time of

The delivered document's age should be computed relative to the time of
the response, not the time of the request.  If the document was not in
cache and the backend took a long time to respond, the document would
end up with a negative computed age, which when printed with %u would
appear as a large positive number (a few seconds short of either 2^32
or 2^64 depending on the size of time_t).

git-svn-id: svn+ssh://projects.linpro.no/svn/varnish/trunk@1142 d4fa192b-c00b-0410-8231-f00ffab90ce4