BibTeX completion via completion-in-region

["Roland Winkler" <Roland.Winkler@physik.uni-erlangen.de>]

Hi Stefan

I noticed that you updated the completion code of BibTeX mode.
Three things:

- Suppose I want to complete the BibTeX string "AB".
  So I hit TAB while point is past the "AB".
  This gives me a buffer displaying possible completions, for example,
  "ABC" and "ABD".
  Then I select "ABC".
  This will insert the complete string "ABC" so that I get the
  awkward result "ABABC".
  I do not know whether this is related to the fact that
  completion-ignore-case is t in that case.
  (Maybe this is a known problem. There are some comments of that
  kind in minibuffer.el.)

- You greatly shortened the code of bibtex-complete-internal by
  calling completion-in-region. The code calling
  bibtex-complete-internal assumes that this function returns the
  completion. This still seems to work, though completion-in-region
  has no documented return value. So I suggest to make the
  completion the documented return value of completion-in-region.

- The return value of bibtex-complete-internal is used by
  bibtex-complete-string-cleanup which displays the expansion of the
  BibTeX string. Yet now this message can be hidden by the `Sole
  completion' message issued by minibuffer-complete. Here I am
  actually not sure what would be the best solution. I like the
  message that tells me the expansion of the BibTeX string (I cannot
  and will never be able to remember their meanings...). But I also
  understand that a "Sole completion' message can be helpful. And I
  know for sure that I am annoyed when one of these message is
  delayed by the other.

If you prefer, I can submit proper bug reports for these things.

Roland