Series constructor doesn't handle object implementing numpy array interface
``` python
In [1]: import pandas as pd
In [2]: import rpy2
In [7]: import numpy as np
In [4]: arr = rpy2.robjects.IntVector(range(10))
In [5]: arr
Out[5]:
<IntVector - Python:0x102ed3908 / R:0x105a7c178>
[       0,        1,        2, ...,        7,        8,        9]

In [6]: pd.Series(arr) # wrong behavior
Out[6]:
0    [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
dtype: object

In [9]: np.array(arr)
Out[9]: array([0, 1, 2, 3, 4, 5, 6, 7, 8, 9], dtype=int32)

In [10]: pd.Series(np.array(arr)) # correct behavior
Out[10]:
0    0
1    1
2    2
3    3
4    4
5    5
6    6
7    7
8    8
9    9
dtype: int32
```

I guess this is a regression due to Series no longer being a subclass of np.ndarray. Not sure if `numpy` exposes a catchall `isarray` that does the checks.
