failing test_moments after centered moving window introduced
I'm getting sporadic failures in
FAIL: test_rolling_std (pandas.stats.tests.test_moments.TestMoments)
FAIL: test_rolling_sum (pandas.stats.tests.test_moments.TestMoments)
FAIL: test_rolling_kurt (pandas.stats.tests.test_moments.TestMoments)
FAIL: test_rolling_max (pandas.stats.tests.test_moments.TestMoments)
and related

git bisected to: 915d261d298c54e887

I've upgraded to  statsmodels  '0.5.0.dev-c9062e4', did a clean/develop
but am still getting failures.

any ideas? @changhiskhan 
