This allows VDPs and VFPs to pass state from a PRIV_TASK to respectively
a vdp_entry or a vfp_entry. When a filter is set up by a VMOD, there is
otherwise no way to configure a filter on a per-task basis.

Closes #3756

Closes #3760

A single tabulation after -cliok or -clierr XXX is enough to align
everything.

Better diff with the --ignore-all-space --word-diff options.

When struct req changed to no longer store its htc, which was somewhat
hidden in a larger seemingly unrelated change, it ended up being
reserved twice. This looks like a case of starting something, being
interrupted, and starting again.

I decided to remove the one sitting between the reservation of VDP and
VFP contexts since the two are related, and this reservation didn't even
initialize htc.

Refs fee476ac

More asserts than strictly needed to catch anything I have missed.

This is preparation to change the enum to a struct.

Relevant to: #3764

Performing the conversion on the stack could lead to a buffer too small
to store the string representation of the IP address. There is no test
case because the error handling is output to stderr.

Refs #3765

And slightly polish the cc_command description.

This is useful for shell script wrappers that can take the original
command as an argument as well as the %{o,s,w} expansions as additional
parameters.

This way the documentation can show neutral defaults for parameters that
are highly platform-dependent.

Similar to PLATFORM_DEPENDENT for things affected by configure options
or other build flags that are not necessarily linked to the target
platform.

With a new %w expansion in the cc_command parameter.

But inject it back into OCFLAGS for distcheck continuity.

And expose bereq.time in vcl_pipe now that we have some.

Refs #3562

fickle for that, and misleading information wastes oceans of time.

They are grouped by categories and that hasn't changed, and the order
of groups haven't changed. All occurrences of foo.* variables are sorted
alphabetically instead of approximately by relationship between each
other.

Inside the first group, variables are now ordered based on the PROXY
protocol diagram:

- client
- server
- remote
- local

A note was added and is hopefully visible enough to maintain this order.

You can verify that nothing changed:

    $ COMMIT=<this-commit-hash>
    $ git show $COMMIT~:doc/sphinx/reference/vcl_var.rst |
      sed '/^$/d' |
      sort |
      sha1sum
    3400130e88c0456b3bc779b9dfeeff09e130efa3
    $ git show ${COMMIT}:doc/sphinx/reference/vcl_var.rst |
      sed '/^$/d ; /.. NOTE:/d' |
      sort |
      sha1sum
    3400130e88c0456b3bc779b9dfeeff09e130efa3

Use whatever alternative to sha1sum your system may provide.