[Groff] floating keep of 2-column text in -ms

[Doug McIlroy]

In -ms, I want a floating keep (KF-KE) to begin with 1-column,
then switch to 2-column text. Of course I want the keep to
float past the following text. It is OK, though, if the keep
does have to float to a new page, for the new page to contain
the kept text and nothing more.

In many tries, I have met an equal number of surprises. I   
won't muddy the issue by enumerating them.

I would welcome any working example. I'd even accept a
suggestion of a different macro package that can peform          
the feat.

In extremis, I can finde the natural page break for the
flowing text and put the kept text right there. But this
is not exactly a robust solution.

Doug