bug#12170: save-excursion fails boundary case with recenter

[Bill Brodie]

>From my point of view (the OP), I've generally used save-excursion to
assemble or manipulate information elsewhere in the buffer or in other
buffers, without explicit reference to window displays.  This seems like a
natural restriction.

I've modified my original code to perform the window operations outside the
form.  Thanks for the illuminating discussion.

-----Original Message-----
From: Eli Zaretskii [mailto:eliz@gnu.org] 

IMO, save-excursion is simply not designed to make sure display isn't
changed in such cases.  It's for excursions into other portions of the
buffer for processing those other parts, without affecting display.
If the processing also scrolls the screen or calls recenter or
otherwise affects the display, all bets are off, because scrolling can
legitimately move point, and when that happens, it is no longer clear
that restoring point should take precedence over window-start etc.