bug#13066: 24.2.90; setting rmail-summary-window-size causes error

[martin rudalics]

> I think it's probably something to do with select-window selecting a
> buffer when it didn't before. At least it looks to me like
> the end of rmail-maybe-display-summary is changing buffer when in 24.2
> it seems not to.

`select-window' now always makes its window's buffer current.  Earlier
it didn't when the window was already selected.  Maybe we should put
this into NEWS as an incompatible change.

> I think this makes the problem go away. Other uses are unaffected AFAICS.

Please install this on the branch.  I neither use rmail nor understand
its treatment of windows.

martin