Isolate context's namespace in modules instead of dicts.
Reflect namespace container changes in cleanup functions.
Positivify negative indices passed to DistArray.__get/setitem__
Positivify local distribution indexes
Add negative indexing tests.
Merge pull request #351 from enthought/refactor/remove-from-global-dim-data

Remove `Context.from_global_dim_data`
Merge pull request #349 from cowlicks/lets-use-modules

Put context's objects in a module instead of a dict.
Merge branch 'master' into cowlicks-indexing
Fixes cleanup code with new namespace management.
Merge pull request #352 from enthought/bugfix-cleanup

Fixes cleanup code with new namespace management.
Merge branch 'master' into refactor/fix-distribution-from-dim-data-per-rank

Conflicts:
	distarray/metadata_utils.py
Merge branch 'refactor/fix-distribution-from-dim-data-per-rank' into bugfix/fix-fromfunction