symbol versioning of private libraries builds

[tridge at samba.org]

Hi Metze,

I'm still thinking about what to do about symbol versions for private
libraries. Please don't make your proposed change yet, give me some
more time to think about it and experiment.

Note that the current behaviour is the equivalent of what we had
before we had symbol versioning (ie. symbols in private libraries are
the same as symbols in public libraries), and we know that it has
worked well. I don't want to make a change where we use separate
symbol naming spaces without thinking about this very carefully.

Cheers, Tridge