Cut the thicket for setting a HTTP response's first line down to just
one function which does what you'd expect.

Start allowing internal VCL use of *resp.status > 999.  The idea
is that we ignore the higher bits but it still has to end up >=
100, so 10404 becomes 404 and 20099 is illegal.   (This change
is not yet complete it will panic if you use it yet.)

More http->failed stuff.
Having wasted half an hour on it (again) it's time to kill the
"response/reason" confusion for good.
More http_ cleanup:

Move policy decisions out where they belong and let the http_Filter
function send the first like through unmolested.

Rather than value specific functions, make a generic
http_ForceField() function, because the name is cool.
Reduce default thread pool size to 10 threads, no need to stress
the pthread implementation in *every* test case.
More struct http polishing