bug#591: 23.0.60; lisp-complete-symbol erases extra text

[Drew Adams]

emacs -Q
 
In *scratch*, type this, and leave cursor after the final `for':
 
format-decode-buffer
forward-char
 
for
 
Then hit `M-TAB'. Choose one of the completions using mouse-2 in *Completions*.
 
Only the final `for' should be completed, but instead all of the text
in the buffer is replaced by the chosen completion.

This is a regression from Emacs 22.
 

In GNU Emacs 23.0.60.1 (i386-mingw-nt5.1.2600)
 of 2008-06-29 on LENNART-69DE564
Windowing system distributor `Microsoft Corp.', version 5.1.2600
configured using `configure --with-gcc (3.4) --no-opt --cflags -Ic:/g/include
-fno-crossjumping'