After trying several different ways, rename vcl_hit{} to vcl_lookup{},
that seems to be the shortest path from A to B.

(Please don't update docs yet, this is just a transition state)
Fold cnt_hit() into cnt_lookup()
Flush the req->vsl on a panic.
Actually do the VSL_flush on panics
Add beresp.uncacheable (will replace beresp.do_pass) and obj.uncacheable
variables.
Move the check for cached uncacheable objs (= "hit-for-pass") into
default VCL.

Add a back-stop, so that a return(deliver) gets turned into return(pass)
with a VCL_Error logged.