`grid_shape` generalized to handle non-distributed dims.

Removes `distdims` and `ndistdim` attributes of LocalArray.

Testsuite updated and passing.
Cleans up paralleltest_localarray.py.
More refactorings relating to grid_shape.
Use `next()` from six.py
Make Python 3 happy.
Merge branch 'master' into feature/generalize-cart-comm
Move BaseLocalArray into localarray.py.
Move utility functions from base to localarray.
Remove base.py.
Rearrange imports.
Move arecompatible function (within file).
Merge BaseLocalArray into LocalArray.
Rearrange imports.
Rearrange imports.
Merge branch 'master' into feature/generalize-cart-comm
Merge branch 'master' into feature/generalize-cart-comm

Conflicts:
	distarray/local/tests/paralleltest_localarray.py
pep8 cleanup.
Add global context at distarray.world.WORLD
Test distarray.world.WORLD exists.
Tests should not "clear" engines.