BUG: fix #3017 Inconsistency in indexing 0-d arrays with Ellipsis.

As mentioned in Issue #3017, there were inconsistencies in the indexing and assignment of 0-d arrays:

    >>> import numpy as np
    >>> a = np.array(1)
    >>> a[...] = 2
    >>> a[...,]
    array(2)
    >>> a[...,] = 3
    Traceback (most recent call last):
      File "<stdin>", line 1, in <module>
    IndexError: 0-d arrays can't be indexed.

The code which checked for special cases omitted this case (of `a[...,]`) so I included it as equivalent to `a[...]`.

Tested in python 2.7.3 and 3.2.3.