"no comment" warnings for non-public entities related to serialization

[Florian Weimer]

* Jonathan Gibbons:

> It would be surprising (bug?) to see a warning being generated for a 
> class that
> is not being documented.  I assume you have not given command-line options
> to include that class in the documentation.  I'm also guessing that this is
> while using javadoc, where the recent change occurred; not javac.
>
> I can also try and recreate the issue, based on what you have said so far.

I can reproduce the issue outside of my strange build environment, so
it should be easy enough to produce a small reproducer.  I'll see if I
can get something to you by the end of the week.