bug#4699: 23.1.50; lisp-complete-symbol erases text

Recipe:  Prepare buffer *scratch* as follows

=== Buffer *scratch* =======================================
;; This buffer is for notes you don't want to save, and for Lisp evaluation.
;; If you want to create a file, visit that file with C-x C-f,
;; then enter the text in that file's own buffer.

(symbol
============================================================

Put point after "(symbol", hit M-TAB (or M-x lisp-complete-symbol) and
in buffer *Completions*  click with mouse-2 on "symbolp".  The buffer
looks now as follows:

=== Buffer *scratch* =======================================
symbolp
============================================================

The problem does not depend on the particular buffer (same problem in
Emacs-Lisp mode buffers) and the particular word to be completed.

The problem does not appear with lisp.el.~1.103~, the version before
the following change:

2009-08-30  Stefan Monnier  <[email protected]>

	* emacs-lisp/lisp.el (lisp-complete-symbol): Use minibuffer-complete.