Closes #2870

Conflicts:
	include/tbl/vsl_tags.h

We can use the NOSUP_NOTICE instead.

Addresses the doc part of #2872.

It's really not obvious, and if it weren't for other tests covering
probes it wouldn't be enough by itself to verify what it needs to.

I was wrong, or I lied. This is the final cleanup.

This time, once and for all.

The due time of the probe which has just finished may be earlier than
the previously earliest due time, so vbp_thread needs to be woken up to
update the nxt value

Fixes #2976

Allow VMOD writers to permit with NULL_OK flag.

Only call object destructor on initialized objects.

Fixes #2839

Conflicts:
	lib/libvmod_debug/vmod.vcc

And make it clear that we steal the reference at this point.

Solaris, (remember Solaris?) will return connection related errnos
on fd metadata operations such as ioctl(2), [gs]etsockopt(2) etc.

We propagated these errors up from VTC_(non)blocking() which could,
theoretically, bail out earlier than it would otherwise have done.
This complicated code far more than it speeded anything up.

Instead just ensure that any errors returned are indeed connection
related, and then ignore them, and let Solaris deal with the broken
connection same way as other operating systems.

Conflicts:
	bin/varnishd/cache/cache_req_fsm.c
	include/tbl/vsl_tags.h

Other SLTs were back-ported as well, but marked as not supported, to
ensure binary forward compatibility up to 6.2 releases.

And we have a goal of making the VSL self-documenting so reordering
anything is pointless. We already reorder SLTs in the documentation
where sorting really matters to end users.

When a VMOD returns a STRANDS, it is a requirement that the storage
be stable, but that is not really different from any other type of
return value.

Completes #2873

Strenghen the case against STRING_LIST in the docs.

See also: #2873

Conflicts:
	lib/libvmod_debug/vmod.vcc

Conflicts:
	lib/libvmod_blob/hex.c

Re-implementations of the current functions for STRING_LIST.

Closes #2733

Conflicts:
	include/vrt.h
	lib/libvmod_debug/vmod.vcc
	lib/libvmod_debug/vmod_debug.c

This introduces VRT 7.1 for the 6.0 releases.

Fixes #2846