Adds `targets` attribute to client Distribution object.
Adds `is_compatible()` to Distribution and maps, client-side.
Refactor _make_intracomm() stuff.
Merge branch 'master' into feature/subset-ranks

Conflicts:
	distarray/dist/context.py
	distarray/dist/tests/test_maps.py
Fix import bug with renamings.
Remove obsoleted method.
Merge branch 'master' into feature/subset-ranks
Refactoring Context comm creation.
Check for compatible distributions in binary_proxy()
Array creation on subset of targets working!

Still have to flesh things out -- this just checkpoints.
context._execute() takes explicit targets.
Merge branch 'master' into feature/targets-per-array

Conflicts:
	distarray/dist/distarray.py
Removes unused method.
Remove extra blank line
Remove trailing blank line from docstrings.
Merge branch 'master' into feature/targets-per-array
Merge pull request #376 from enthought/feature/targets-per-array

Allow Distribution and DistArrays on subset of targets