converted multi-context with-statements to nested (2.6 compatibility)
moved DummyMod to proper namespace to enable pickling
Revert "converted multi-context with-statements to nested (2.6 compatibility)"

This reverts commit 311acdf45e9d164ac3dd3eb72b913dfc7d7e4314.
added undoc and made DummyMod doc more reflective of context
Merge pull request #4186 from mmckerns/master

moved DummyMod to proper namespace to enable dill pickling