basic usage of C4::Circulation::AddIssue

Note: This logic is repeated in KohaTest::Circulation::checkout_first_item, but without tests. This includes tests at each step to make it easier to track down what's broken as we go along.


Make sure that we can set the issuedate of an issue.

Also, since we are specifying an issuedate and not a due date, the due date should be calculated from the issuedate, not today.