COMPAT: numpy compat with array methods in >= 1.7
This is and API change in  numpy >= 1.7, but need to work around. Numpy now
looks at the structure for a p`rod` method (if the function is not operating on a numpy array), if it has one, then it passes the arguments
`axis,dtype,out`, currently these types of methods only aceept `axis`, need to accept `dtype,out` as dummy arguments for compat

affects `mean,sum,prod,std`...prob others

```
In [1]: df = DataFrame(randn(10,2))

In [2]: np.prod(df)
---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-2-99feb18ea783> in <module>()
----> 1 np.prod(df)

/usr/local/lib/python2.7/site-packages/numpy/core/fromnumeric.pyc in prod(a, axis, dtype, out, keepdims)
   2111             return _methods._prod(a, axis=axis, dtype=dtype,
   2112                                 out=out, keepdims=keepdims)
-> 2113         return prod(axis=axis, dtype=dtype, out=out)
   2114     else:
   2115         return _methods._prod(a, axis=axis, dtype=dtype,

TypeError: prod() got an unexpected keyword argument 'dtype'

In [3]: np.prod(df.values)
Out[3]: -2.2566177751865827e-07

In [4]: np.prod(df.values,axis=1)
Out[4]: 
array([-0.00912739,  0.00569453,  0.58508784,  0.87462665, -0.32556754,
        0.12015118,  1.01860104, -0.15380337, -0.54518287, -2.5393832 ])
```
