Add AddeJythonDayRequiredError exception. [1682]

ADDERROR.DOC doesn't give an error code for this situation; currently
using -1000.
Fix AddeJythonError's __str__ method. [1682]

This resolves the "NoneType" error that happens when trying to print out
a non-subclassed AddeJythonError that does not have an error message.