[biblio] Relative paths and BIBINPUTS

[Karl Berry]

Hi Tohiko - I admit I did not try to reproduce your problem (thanks for
the careful report and scripts; much appreciated), because I saw this in
your mail:

    only when the path starts with `..` (or `.`).

I made the decision when I wrote kpathsea that if a filename started
with an explicit "." or "..", it would be treated as an absolute path
(same as if it started with "/" or "C:" or whatever), and only looked up
as-is, not along the search paths.  Normal shells do it that way, so it
seemed like this was the most intuitive thing to do.

I wouldn't claim that the entire TeX suite is 100% consistent in this
regard, but I think that might explain the behavior you're seeing?
--thanks, karl.