data type "datetime" not understood
When building pandas 0.19.2 or 0.20.3 I get many similar test failures.

Here is one from the attempt to build 0.19.2:

```
======================================================================
ERROR: test_timedelta64_equal_timedelta_supported_ops (pandas.tests.series.test_operators.TestSeriesOperators)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/tmp/guix-build-python-pandas-0.19.2.drv-0/pandas-0.19.2/pandas/tests/series/test_operators.py", line 570, in test_timedelta64_equal_timedelta_supported_ops
    lhs = op(ser, nptd)
  File "/tmp/guix-build-python-pandas-0.19.2.drv-0/pandas-0.19.2/pandas/core/ops.py", line 696, in wrapper
    converted = _Op.get_op(left, right, name, na_op)
  File "/tmp/guix-build-python-pandas-0.19.2.drv-0/pandas-0.19.2/pandas/core/ops.py", line 330, in get_op
    return _TimeOp(left, right, name, na_op)
  File "/tmp/guix-build-python-pandas-0.19.2.drv-0/pandas-0.19.2/pandas/core/ops.py", line 343, in __init__
    lvalues = self._convert_to_array(left, name=name)
  File "/tmp/guix-build-python-pandas-0.19.2.drv-0/pandas-0.19.2/pandas/core/ops.py", line 454, in _convert_to_array
    if (inferred_type in ('datetime64', 'datetime', 'date', 'time') or
TypeError: data type "datetime" not understood
```

I get these errors with python-dateutil 2.6.0 as well as 2.6.1.  Could you please confirm that the tests pass when building with python-dateutil 2.6.x?

I'm building with Python 3.5.3.