[pdftex] kpathsea environment variables

[Karl Berry]

    The question is how should this tool decide what is a kpathsea
    variable and what is not?

    query kpathsea to find out which language level arrays should be 
    interpreted as kpathsea environment variables.

Seems extending the output of kpsewhich --help to include the basic
envvar names would probably suffice, do you agree?  I can't think of
anything else feasible to do.

It won't be perfect because the envvar list can vary with the
application and/or actual argv[0], and it seems like these tools might
not know the application being used (dvips vs. xdvi vs. tex vs. ...)
But those envvars tend to be fairly obscure anyway, so it would probably
be a useful subset to just get the generic ones.

k