BUG/ENH: Passing explicit dtype should delegate to appropriate Index subclass (if available)

[jtratner]

e.g. here's wrong behavior on current master

In [1]: import pandas as pd
In [2]: ind = pd.Index([1, 2, 3], dtype='int64')
In [3]: ind
Out[3]: Index([1, 2, 3], dtype='object')

Problem is ordering of how passed dtypes work in Index constructor. Make sure this gets fixed in 0.14.

[jtratner]

I'm punting this to 0.14 - too much of internals rely on this behavior right now and it's clearly not that big of a deal. I think it may just resolve itself when index isn't ndarray (because I think it's either hitting weirdness with numpy methods OR there's a case where we expect to be passing values are are instead passing Index)

[sinhrks]

Closed by #11017.