Error in test suite for timedelta operations
This is on the VM running pandas windows builds.
Windows XP
Python 2.7 32-bit
numpy 1.7.1

```
======================================================================
ERROR: test_timedelta_ops_with_missing_values (pandas.tseries.tests.test_timedeltas.TestTimedeltas)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "C:\workspace\pandas-windows-test-py27\pandas\tseries\tests\test_timedeltas.py", line 247, in test_timedelta_ops_with_missing_values
    actual = s1 + timedelta_NaT
  File "C:\workspace\pandas-windows-test-py27\pandas\core\ops.py", line 461, in wrapper
    time_converted = _TimeOp.maybe_convert_for_time_op(left, right, name)
  File "C:\workspace\pandas-windows-test-py27\pandas\core\ops.py", line 428, in maybe_convert_for_time_op
    return cls(left, right, name)
  File "C:\workspace\pandas-windows-test-py27\pandas\core\ops.py", line 246, in __init__
    rvalues = self._convert_to_array(right, name=name, other=lvalues)
  File "C:\workspace\pandas-windows-test-py27\pandas\core\ops.py", line 363, in _convert_to_array
    " operation".format(pa.array(values).dtype))
TypeError: incompatible type [timedelta64[ns]] for a datetime/timedelta operation
```
