[tlbuild] kpsewhich problem [Cygwin]

[Karl Berry]

    +      /* Some trickery here: the extensions for kpse_fmt_format can
    +       * clash with other extensions in use, and we prefer for those
    +       * others to be preferred.  

Ok, I'll revert that change, but I don't understand it.  The only
extension for kpse_fmt_format is .fmt.  How does that clash with
anything?  .fmt is not used for anything else.

Olaf, if you happen to see this ... ?