bug#10348: 24.0.92; Save and load window states

[Stefan Monnier]

> The former would explicitly name the parameters that have to be
> preserved accross window configuration changes.  The latter would be
> responsible for not writing out parameters to disk.

It seems that we indeed need to distinguish window-states for
inter-session use and for intra-session use (e.g. via the `markers'
argument).

And of course the parameters preserved intra-session is a superset of
the parameters preserved inter-sessions.

Using window-state-ignored-parameters to specify the difference between
the two sets seems OK.

> This approach is inconsistent if `window-state-saved-parameters' changes
> within the body of the `save-window-excursion'.

Indeed, it's a bit ugly.  An alternative would be to ignore
window-state-saved-parameters (and window-state-ignored-parameters)
upon restore.  Instead, we'd save the parameters in a list where each
element is either (PARM . VAL) or just PARM where the second form
indicates that PARM was not set and should hence be unset upon restore.


        Stefan