concurrent -C tests don't collided.

Problem spotted by:	fgs

Fixes:	#1802

In 5c826806 the checks are relaxed,
but this commit (or part of) was not brought into 4.1.

Fixes: #1842

try to delete a objhead while it still has a waiting list,
by forcing the last ref holder to rush the WL.

Since the hasher owns the refcounts on objhead, we cannot just
mingle req and objcore refcounts.

Fortunately we don't need to add another refcounter, because all
we really care about is the wl being empty when we drop the last
ref.

The wl/hsh_rush() mechanism will work differently with different
thread-scheduling schenarios, and I cannot definitively rule out
that we can drop the last ref on an oh, while there are still req's
on the waiting list.

Given that, and the existence proof in ticket #1823's race, this
might have been the indicated memory-trampler.

Conflicts:
	bin/varnishd/cache/cache_hash.c

The latter takes precedence as per RFC 7232.  Also if we have an I-N-M
but no entity don't check I-M-S, just do a non-conditional request.

Conflicts:
	include/vrt.h

This paves the way towards failing VCL_EVENT_WARM events in VMODs. If
setting the temperature fails, we may need to carry a message back to
the CLI and other bits of context.

	import vmod from "/some/dir/"

and have the default vmod shlib filename appended.

know the filename of the -f argument, it should be possible to
include "./" relative to it.

The footnote is that the include is resolved at lower privlevel
than the -f file is read, so in really obscure cases you could
have really obscure error messages.

VCL file, and illegal everywhere else.

This makes it easier to distribute "VCL-packages"

Test-case written by:	Kacper

the VCL fileopening logic in mgt so we have it only one place.

away const.

for more clarity, before we start hacking VCC further.

all other methods use rdlock

Submitted by:	github::onovy

In the 304 case we were already skipping it for non-zero C-L.
For 204 responses this was introduced as a side effect of 271e1c52.

Fixes:	#1823

for 5 seconds if there is a waiting list.

This allows the waiting list to drain (returning 503) quickly,
rather than one by one trying to pester the backend and only
giving up after the connect_timeout.

Related to: #1823

new improved probability of getting the VSL out.

That obscured problems in cleanup

The script lacked a logexpect -wait at the end telling it to actually
wait for the required log content.

Added a new rule to match first on an actual retry backend transaction
and match the header set/unset/set tests on that vxid.