Checking for purge prevents caching

[Anton Stonor]

Just to share the conclusion on my issue on Varnish restaring 
unpredictable with an innocent snippet of VCL:

sub vcl_hit {

     if(req.http.Cache-Control == "no-cache") {
         set obj.ttl = 0s; error 200 "Hey, we got a purge";
     }
}

I have not been able to reproduce it in another environment and with the 
latest Varnish. So consider issue #92 bogus.

/Anton