[Orgmode] In-buffer completion

[Carsten Dominik]

Dear all,

yesterday I replaced the previous implementation of
in-buffer completion (M-TAB of Esc TAB) with a new
function making use of John Wiegleys pcomplete.el.
In fact, John did most of the Org-related implementation
already months ago - I only tied up some loose ends.

So if you are noticing something unexpected in
in-buffer completion, this is the cause.  There may
be bugs, if you find any, let me know.

Most importantly, however, in-buffer completion is now
implement so much cleaner, and we can extend it if we
want.  So if you have good ideas where in-buffer completion
would be useful and does not work already, lets hear it!

Thanks to John for yet another great addition to Org mode.

- Carsten