COMPAT: numpy compat with array methods in >= 1.7

[jreback]

This is and API change in numpy >= 1.7, but need to work around. Numpy now
looks at the structure for a prod 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 ])