Attempt to free unreferenced scalar during global destruction

[kiwiroy]

This was raised and reproduced on dbi-users, thanks @ronsavage.

I've written a further test for this which is more simple and passes far less options to connect() to aid in identification of the cause and could possibly be made subject of a pull request.

observations

• In the monkey patched DBD::CSV::Table::DESTROY uncommenting this stops the warnings.
• Specifying csv_tables is a sure way to trigger the warning, however I have seen multiple warnings from this code, from the test_with_options() for (1 .. 100); calls, so I doubt this is the full story.
• The SV that is unreferenced is always the Text::CSV_XS object, so I don't know if the bug lies there - csv_tables is not an option to new() there though.

[Tux]

@rehsack You promised to have a look. This is just a reminder. See https://github.com/perl5-dbi/DBD-CSV/tree/master/sandbox/issue-4 for test files