(refer-bib-directory): New variable, list of

(refer-bib-directory): New variable, list of
directories where to look for bib files.  Special values `texinputs'
and `bibinputs' mean take directory list from corresponding
environment variable.

(refer-bib-files): New special value `auto', for looking up all
files in directories pointed to by refer-bib-directory.
I have the feeling that this isn't really my code but came from
the net (copylefted). However, I cannot trace this down any
more. If it isn't mine, it's probably Ashwin's.
(refer-get-bib-files): Support `auto' value of refer-bib-files.
Support `texinputs', `bibinputs' value of refer-bib-directory.

(refer-saved-state, refer-previous-keywords, refer-saved-pos,
refer-same-file): Properly declared (defvar) these variables.

(refer-yank-key): New function.

(refer-find-entry-internal): Find bibliography entries in other
window, with minimal reconfiguration of windows.

(refer-expand-files): New function.