varnish debugging output a separate log handle.

(The point here is to maximize the amount of concurrency we can
simulate.  Down the road, the logging may become pre thread with
a final sorting pass to get all the messages correctly interleaved.)



git-svn-id: http://www.varnish-cache.org/svn/trunk/varnish-cache@2775 d4fa192b-c00b-0410-8231-f00ffab90ce4