[GH#4] Understand Varnish 3.x VCL_call + return

In Varnish 3.x, VCL_call can report call name and return value
together in the same log line.

Make sure we handle that, otherwise our HIT/MISS detection code
fails miserably.
Now works with Varnish 3.x
We're not using the req counter per client for now