COMPAT: can we reduce pathological cases in Index comparisons
from [SO](http://stackoverflow.com/questions/37444307/equality-of-pandas-index-objects-with-different-dtypes-and-elements/37444423#37444423)

```
In [1]: i1 = pd.DatetimeIndex(['1971-10-01'], dtype='datetime64[ns]', freq=None)

In [2]: i2 = pd.Index([u'100171'], dtype='object')

In [3]: i1
Out[3]: DatetimeIndex(['1971-10-01'], dtype='datetime64[ns]', freq=None)

In [4]: pd.DatetimeIndex(i2)
Out[4]: DatetimeIndex(['1971-10-01'], dtype='datetime64[ns]', freq=None)
```

We _might_ be able to elminate the coercion in `.equals()` in some cases.
