bug#12670: 24.2.50; Uncustomizable defcustom

[Chong Yidong]

Katsumi Yamaoka <yamaoka@jpl.org> writes:

> Oops, you're right.  I don't recall why I said it's uncustomisable,
> but please let me rephrase it:
> That defcustom form is unable to suggest a default value, that's
> the one suitable to beginners for example, to a user.  Could you
> try the following two examples?  Both behaviors should be the same.
> And my patch solves it.

Ah, OK.  Looks fine to me, please go ahead and commit to trunk.