Exception With np.frompyfunc
from aqr.core.frame import DataFrame
import numpy as np
def func(a, b):
    return a + b
df = DataFrame({'US':[1,2,3]})
f = np.frompyfunc(func, 2, 1)
print f.accumulate(df)

In pre-0.4.0 pandas, this printed:
   US
0  1
1  3
2  6

Now, this:
ValueError: could not find a matching type for func (vectorized).accumulate, requested type has type code 'q'
