bug#13568: 24.3.50; wishlist: add a `group-p' predicate

[Drew Adams]

> >> > Subject line says it all: Please add a predicate `group-p' that
> >> > returns non-nil if its symbol arg is a loaded customize group
> >> > (i.e. defined by a defgroup that has been evaluated).
> >>
> >> What the use case for such a function?
> >
> > Uh, to test whether a given symbol corresponds to "a loaded
> > customize group (i.e. defined by a defgroup that has been
> > evaluated)."
> 
> And what's the use case for that?  Why do you want to know whether a
> symbol has been used as a customization group?

Why wouldn't I?  A custom group is a thing.  If you have
code that uses that thing (and that is what the thing
is for) then it is reasonable to be able to test for
that thingness.