Large scalar powers hang


```
In [57]: np.int64(2)**(2**62)
Out[57]: 0

In [58]: np.int64(2)**(2**63)
<ipython-input-58-7f1b37f891d0>:1: RuntimeWarning: overflow encountered in power
  np.int64(2)**(2**63)
Out[58]: inf

In [59]: np.int64(2)**(2**64)
# seems to be doing the computation on object arrays?

