Made errors more Python version-independent.
Made errors more Python version-independent.

jvalleroy/plinth-debian,harry-7/Plinth,vignanl/Plinth,jvalleroy/plinth-debian,kkampardi/Plinth,harry-7/Plinth,jvalleroy/plinth-debian,freedomboxtwh/Plinth,freedomboxtwh/Plinth,harry-7/Plinth,vignanl/Plinth,freedomboxtwh/Plinth,freedomboxtwh/Plinth,vignanl/Plinth,harry-7/Plinth,kkampardi/Plinth,kkampardi/Plinth,freedomboxtwh/Plinth,vignanl/Plinth,vignanl/Plinth,harry-7/Plinth,kkampardi/Plinth,kkampardi/Plinth,jvalleroy/plinth-debian,jvalleroy/plinth-debian