BUG: Fix copy s.t. it always copies index/columns.

Only copies index/columns with `deep=True` on `BlockManager`. Plus some
tests...yay!

Change copy to make views of indices.

Requires changing groupby to check whether indices are identical, rather
than comparing with `is`. Plus add tests for name checks through
everything.

Add some views with data copying...
ENH: enable deep copy for sparse Series/Panel
ENH: Add 'is_' method to index.
More tests for is_