Undefined $DBI::errstr on execute fail on Windows

This is actually a very important fix, without this errstr is not set on Windows!

It has been reported here:
https://rt.cpan.org/Ticket/Display.html?id=71047 - "Undefined $DBI::errstr on execute fail on Windows-7-x64"
https://rt.cpan.org/Ticket/Display.html?id=83353
http://bugs.activestate.com/show_bug.cgi?id=91026
http://lists.mysql.com/perl/4415
http://stackoverflow.com/questions/7432944/undefined-dbierrstr-using-dbi-perl-and-mysql-on-windows-7-x64
http://blogs.perl.org/users/mithaldu/2011/10/dbdmysql-4019-and-4020-are-broken-on-win32-heres-how-to-downgrade.html