(bibtex-pop): New generic function which unifies the

(bibtex-pop): New generic function which unifies the
functionality of bibtex-pop-previous and bibtex-pop-next.  Now,
bibtex-pop moves to the end of field after the pop.  Concatenated
strings are now handled correctly.  Delimiters are not added to
non-delimited entries.  Changed occurences of
bibtex-text-in-cfield to bibtex-text-in-field.
(bibtex-pop-previous, bibtex-pop-next): Call bibtex-pop.
(bibtex-complete-string): Fixed bug that removed delimiters
around the following field if current field is already
undelimited on completion.
(bibtex-complete-string, bibtex-remove-double-quotes-or-braces):
Only remove delimiters if field text is not concatenated.
(bibtex-font-lock-keywords): Use the same regexps used
in all other places of bibtex.el to parse the buffer.
(bibtex-mode): Changed the definition of font-lock-defaults,
so that quote-delimited entries aren't fontified as strings anymore.
(bibtex-parse-keys): Changed the regexp used for finding crossref entries.
(bibtex-field-const, bibtex-reference-key): Fixed the regexp
to match more of the characters allowed here by BibTeX/LaTeX.
(bibtex-field-name): Made it less restrictive.
(bibtex-field-string): Changed so that quote-delimited entries
with quotes inside aren't a problem anymore.  Changed nesting
level of braces in entries to support three inner braces.
(bibtex-validate-buffer): By giving an optional argument, the
user can now let it not validate the whole buffer, but only
the portion starting at point.  Small modification in strategy
used to find next entry.
(bibtex-print-help-message): Ignore case in field name when
searching for help text.
(bibtex-submit-bug-report): New function.