bug#19170: 25.0.50; enhancement request: `compare-windows' use across frames

[Juri Linkov]

> And maybe print the point values too, unless they're the same buffer?
>
> Different, A: 2349, B: 1358
> Same: A: 2349, B: 1358
> No match

Or the size of the region of difference or sameness.

> Dunno what the names might be.  They could be the buffer names
> (possibly truncated, if long), if different.

There is no displayable information associated with windows
other than buffer names.

>> We already have a lot of `last-...' variables, so a new variable
>> for the last selected window makes sense.  Then it would be
>> convenient to compare `(selected-window)' with `last-selected-
>> window'.
>
> Please do.

There are still open questions about this new variable, e.g.:
what should be recorded in `last-selected-window' in case of
`C-x 0' (`delete-window') when the last window is deleted?