Failing test on win/py2.6/64, TestResample:test_how_lambda_functions
This has failed intermittently a couple of times in the last week or two.

```
=============================================================
=======================
FAILURE: test_how_lambda_functions (pandas.tseries.tests.test_resample.TestResample)
------------------------------------------------------------------------------------
Traceback (most recent call last):
  File "c:\Python27-AMD64\Lib\unittest\case.py", line 331, in run
    testMethod()
  File "C:\workspace\pandas_tests\BITS\64\PYTHONVER\27\pandas\tseries\tests\test_resample.py", line 640, in test_how_lambda_functions
    tm.assert_series_equal(result['bar'], bar_exp)
  File "C:\workspace\pandas_tests\BITS\64\PYTHONVER\27\pandas\util\testing.py", line 448, in assert_series_equal
    assert_almost_equal(left.values, right.values, check_less_precise)
  File "testing.pyx", line 58, in pandas._testing.assert_almost_equal (pandas\src\testing.c:2561)
  File "testing.pyx", line 93, in pandas._testing.assert_almost_equal (pandas\src\testing.c:1803)
  File "testing.pyx", line 107, in pandas._testing.assert_almost_equal (pandas\src\testing.c:2023)
AssertionError: First object is not null, second is null: inf != nan
```
