BUG? Inconsistent index type inferencing for mixed integer/floating, index=list vs index=Index(list)
Index type inference produces two different results for a list of mixed integers/floats depending on whether index is provided to the DataFrame constructors as a list directly or first constructed using the Index constructor (this in turn leads to very different indexing behavior)

```
In [2]: df=p.DataFrame(["a", "b", "c", "d", "e"], index=[1.0, 2.5, 3, 4.5, 5.0])

In [3]: df.index.inferred_type
Out[3]: 'floating'

In [4]: df=p.DataFrame(["a", "b", "c", "d", "e"], index=p.Index([1.0, 2.5, 3, 4.5, 5.0]))

In [5]: df.index.inferred_type
Out[5]: 'mixed-integer-float'
```
