Added test for RT45684.
Minimum perl version is now 5.8.1, just as for DBI.
Added test for RT29363.

See https://rt.cpan.org/Ticket/Display.html?id=29363

Reporter mentioned the warnings in $dbh->{info} and
$sth->{mysql_warning_count} could differ.

I could not longer reproduce this with the given code sample.

I added the code snipped from the RT ticket to t/29warnings.t
to extend the test suite.
Use 'use strict; use warnings;' everywhere.