Happy new year!

This reverts commit de3e581e.

tests/saintmode/test04.vtc from varnish-modules revealed that there may
be use cases where it is implied that vcl_backend_error will leave a
ttl=0 object and the sale object will remain in place.

This can be resolved by:

	- return(abandon) for these cases or
	- making the HSH_Kill conditional on bo->fetch_objcore->ttl > 0

but I already has concerns regarding the impact of this change and have
them even more now.

We need time to ponder about the consequences and a documented
inefficiency is better than unexpected behaviour in a release.

Our stack space canary in v00004.vtc fell off the twig on fedora rawhide
i686

Thank you to @ingvarha for testing, reporting and all your support
overall!

Fixes #2946 in the sense that we want to treat backend synth like any
other object and kill the stale object it replaces.

The two HSH_Kill calls could also be subsumed in vbf_fetch_thread(),
but after an irc discussion, phk decided that he wanted to aim for even
more consolidation later.

The test checks that we remove the stale_oc, but not when abandoning the
bereq.

I'm keeping that information in both the changes and upgrading documents
to increase the chances that people will notice it.

The imprecise "changes" statement predated the decision to drop Python 2
entirely and was spotted by Geoff.

Reported by coverity.

Unless we think of something else to add, this version of the docs
is suitable for the 6.2 release.

Fixes #2943

Patch by @phk, test by yours truly.

See dd28fc73 for the whole story.

Dealing with code style violations around the return keyword, I figured
I could automate that fix, so I tried with my favourite refactoring tool
and following those steps:

    $ cat >return.cocci <<EOF
    @@
    expression rv;
    @@

    - return rv;
    + return (rv);
    EOF
    $ spatch --dir . --in-place --sp-file return.cocci

Unfortunately that leads to proper return statements having their return
value enclosed twice, like `return ((rv))`. So a bit more steps to go:

    $ cat >rereturn.cocci <<EOF
    @@
    expression rv;
    @@

    - return ((rv));
    + return (rv);
    EOF
    $ spatch --dir . --in-place --sp-file rreeturn.cocci

At this point you don't want to touch bundled code, right? So let's take
care of libvgz and shout out to teken that saw no changes at all!

    $ git checkout -- lib/libvgz/

The next step is to manually review all the changes, because Coccinelle
is not aware of how we break lines and unbreaks them. That's quite
tedious but I was waiting for someone and they are still late as I'm
describing the whole process.

Care was taken not to touch varnishtest to make it easier to sync with
vtest. A dedicated patch will follow.