bug#64536: 30.0.50; Make cl-print put buttons on ellipses

[Stefan Monnier]

> However, other users of `backtrace-ellipsis' button may be affected if
> they used it for different purposes.

That's also what I thought at first, but the case of `inspect.el` made
me realize that it's likely that just letting them use
`backtrace-ellipsis` button is often not the right solution anyway.

> May it be possible to create an obsolete alias for this button type?

And I don't think we have such aliases.


        Stefan