one for each VCL method to record the return
	one for errors
	one for linking a client session to a backend connection
Use them sensibly.
Put VCL name of backend into struct backend to improve log messages



git-svn-id: http://www.varnish-cache.org/svn/trunk@223 d4fa192b-c00b-0410-8231-f00ffab90ce4