This is the number of good probes we pretend to have already seen when
we start up, in order to speed up getting healthy backends.

The default value is one less than the .threshold, so the backend
will be set healthy if it manages to respond correctly to the very 
first probe we send to it.

(A bit of this commit leaked in during r4184)



git-svn-id: http://www.varnish-cache.org/svn/trunk/varnish-cache@4185 d4fa192b-c00b-0410-8231-f00ffab90ce4