bug#35873: Add atomic window support to Gnus

[martin rudalics]

> I updated the patch with Martin's suggestion, and am back to running
> this daily. One thing I noticed is that (in this case in my Gnorb
> package) running `delete-other-windows' from a Gnus window will now
> result in one of these:
>
> delete-other-windows: Root of atomic window is root window of its frame
>
> That error is expected with atomic windows. I can change Gnorb to not
> use `delete-other-windows' (it shouldn't be using that anyway), but I
> wonder if that's likely to cause an unacceptable amount of friction with
> other packages/user code. (While noting that this behavior is off by
> default.)

You can also specify a function in the 'delete-other-windows'
parameter of any window involved.  One that dissolves atomicity, for
example.

martin