Cannot ingest a numpy array if type datetime64

[st-pasha]

import numpy
import datatable as dt
a = numpy.zeros(dtype="<M8[s]", shape=(10,))
d = dt.Frame(a)

raises ValueError: cannot include dtype 'M' in a buffer.

The expected behavior is that this column gets converted into strings; and when the datetime type is implemented, it should be converted into a datetime column.