print traceback on IntegrityError exception
print traceback on IntegrityError exception

there is a not-very-clear exception (IntegrityError) raised when
calling the save() method, due to the mis-configuration of
transitions data (that should be omitted, at the moment, btw).

openpolis/open_municipio,openpolis/open_municipio,openpolis/open_municipio,openpolis/open_municipio