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

[Stefan Monnier <monnier@iro.umontreal.ca>]

forcemerge 16728 16752
thanks

> Evaluating this expression returns:
> (list deactivate-mark
>       (pp-to-string '1)
>       deactivate-mark)

deactivate-mark is a global variable and lots of functions happen to
work on internal buffers, which ends up "unwittingly" setting
deactivate-mark to t.

There are 2 directions to try and fix it:
1- let-bind deactivate-mark in functions like pp-to-string so as to
   eliminate those spurious deactivations.  But there can be many of
   them, and it doesn't solve the problem where the buffer-modification
   is done in a non-temporary buffer.
2- make deactivate-mark buffer-local.  This is "The Right Way" but
   might introduce new problems.
   E.g. we really should deactivate the mark in all the buffers that
   have their deactivate-mark set.


        Stefan