[PATCH 3 of 3] template: unify template output to use abspath (BC)

[timeless]

Yuya Nishihara wrote:
>
> Instead of abusing "sep", I would do:
>
>   abspathindex = ...  # index in fields
>   ...
>   for f, p, l:
>       ...
>       if abspathindex >= 0:
>           fm.data(file=p[abspathindex])

I couldn't come up w/ a good approach to this, I'm happy to take yours.
I also wanted it to be somewhat scalable in case it happened again,
but, I think I should let someone else cross that bridge when they
come to it.