Adds workaround to remove empty local arrays

Slices the distribution object to remove all empty localarrays before
returning.  Only done if all dimensions use 'b' or 'n' in the dist
tuple.

Generalizes the fix in PRs #444 and #447.
Merged.  I think it barfed because I don't call `sanitize_indices` inside
`Distribution.slice`-- I call it before calling `Distribution.slice`.


On Mon, Jul 7, 2014 at 4:02 PM, Kurt Smith <notifications@github.com> wrote:

> In distarray/dist/maps.py:
>
> > @@ -612,7 +612,17 @@ def __new__(cls, context, shape, dist=None, grid_shape=None, targets=None):
> >
> >          # list of `ClientMap` objects, one per dimension.
> >          maps = [map_from_sizes(*args) for args in zip(shape, dist, grid_shape)]
> > -        return cls.from_maps(context=context, maps=maps, targets=targets)
> > +
> > +        self = cls.from_maps(context=context, maps=maps, targets=targets)
> > +
> > +        # TODO: FIXME: this is a workaround.  The reason we slice here is to
> > +        # return a distribution with no empty local shapes.  The `from_maps()`
> > +        # classmethod should be fixed to ensure no empty local arrays are
> > +        # created in the first place.  That will remove the need to slice the
> > +        # distribution to remove empty localshapes.
> > +        if all(d in ('n', 'b') for d in self.dist):
> > +            self = self.slice((slice(None),)*self.ndim)
>
> Yeah, I tried Ellipsis, but it barfed. So this is the workaround for the
> workaround.
>
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