bug#20900: 25.0.50; C-u - C-t should move point backward to have a usefully repeatable command

[Nicolas Richard]

In a line like this:
aaaaaaaaxy
with cursor on y (i.e. point is between x and y).

Hitting C-u - C-t moves the 'x' backwards, but the cursor stays on 'y'.
Thus hitting C-x z is mostly useless here. I expected cursor to move
backward too.

In fact this is a regression introduced by

commit aa26f345096166bd8c135876dbab9b671ae232e3
Author: Chong Yidong <cyd@gnu.org>
Date:   Fri Dec 21 13:42:59 2012 +0800

    * simple.el (transpose-subr-1): Preserve marker positions
    by changing the insertion sequence.
    
    Fixes: debbugs:13122