bug#16752: 24.3.50; pp-to-string deactivates mark

[Eli Zaretskii]

> From: Helmut Eller <eller.helmut@gmail.com>
> Date: Fri, 14 Feb 2014 10:46:08 +0100
> 
> Evaluating this expression returns:
> 
> (list deactivate-mark
>       (pp-to-string '1)
>       deactivate-mark)
> 
> returns (nil "1" t).  Deactivating the mark is a surprising and
> unnecessary side effect.

_Any_ change to _any_ buffer will set deactivate-mark, which is a
global variable.