Show source index in VCL_trace

[Dridi Boukelmoune]

> I thought 2 pattern solution.
>
> - Add vcl source index in vcl_trace.
> https://github.com/varnishcache/varnish-cache/compare/master...xcir:patch/modify_vcl_trace?expand=1
>
>    32770 VCL_trace      c 1 2.3.3
>    32770 VCL_trace      c 2 2.4.5
>                           | | | |
>                           | | | +---- VCL program line position
>                           | | +------ VCL program line number
>                           | +-------- VCL program source index
>                           +---------- VCL trace point index

Usually when we add a field to a record, it's appended to avoid
breaking existing programs already relying on the existing fields.

> - Add -t(trace) option in vcl.show
> https://github.com/varnishcache/varnish-cache/compare/master...xcir:patch/add_t_opt_cli?expand=1
> This patch dumps VGC_ref.
>
>    $ sudo varnishadm vcl.show -t boot
>    index src  line  pos token
>        1   2     3    3 "if"
>        2   2     4    5 "std.log"
>    ...
>       36   1   189    5 "return"
>       37   1   193    5 "return"
>
> I think modify to vcl_trace is better.
> But, VSL format change is painful.

I think we discussed this at some point and another solution was to
reference line numbers from the output of `vcl.show -v` that already
contains the whole VCL, including the built-in and the includes.

> I'll like to create either pull-request.
> Can I get your opinion?

I will mention this during today's bugwash, I'm not sure you can
attend given your timezone.

Cheers