Driver private functions, prefix and inheritance

Hi Tim,

during the update of DBD::AnyData I hit some nice methods, which Jeff has 
added to it, e.g. ad_get_catalog, ad_mod_catalog and ad_clear.

These methods modify the meta data of the tables managed by DBD::AnyData
(DBD::AD) which will be done by DBD::File in future releases. So I talked
with Merijn to move the methods into DBD::File to have them common for
- DBD::AnyData
- DBD::CSV
- DBD::DBM
- DBD::PO

But now it comes ... typically driver private methods require a prefix.
This prefix depends on the driver name (so ad_* for DBD::AD methods, csv_*
for DBD::CSV methods etc.) - and it would be good for DBD::* users when
we keep/support this behaviour.
 From  this  it  follows  that it's not done by moving the methods with some
refactoring to DBD::File and install them by their name in DBD::File - there
should be a better way.

Any suggestions?

Jens