Refactoring DBD::File in preparation for ReadOnly and streams ...

Hi Merijn,

while hacking around in DBD::File and DBI::DBD::SqlEngine I stumbled
over a major design fault made in the past:

sub DBD::File::Table::get_table_meta () ... evaluates
$dbh->{f_meta}{$table}{initialized} and does something magic else. This
magic is fully DBD::File addicted (heavily relies on file2table) and it
should be broken into separate pieces to differ between initialisation
done for DBI::DBD::SqlEngine and DBD::File and DBD::DBM ...

I'd like to discuss it tomorrow in IRC (but I read my e-Mail if you have
comments at the evening).

If anyone else has ideas - please feel free to speak (but primary
restriction is backward compatibility to avoid breakage of dependent DBD's).

Best regards,
Jens