Restore slots support for SecurityOptions, omitting those attributes already served by properties. Better fix for #103 that assumes there was a purpose intended by the original slots.

--HG--
extra : source : 44ea31b0719e1387533b95d871e62525fb74514a
Update travis.yml to reflect new target versions

--HG--
extra : source : 76236999e08b261f6f174bb9057046bb0d80c1d2
Declare dependency on six

--HG--
extra : source : e2d079b555a787d96ef2f688b5e56e9e7dada322