I have no idea how I overlooked that a "bytes=-100" range was from the
end of the object, but I did.

Fixes #704.

Reported by:    Luc Saillard



git-svn-id: http://www.varnish-cache.org/svn/branches/2.1@5025 d4fa192b-c00b-0410-8231-f00ffab90ce4