add comment to test in sandbox that sometimes fails at given precision,  current test status: 584 tests  KNOWNFAIL=5, SKIP=40, fail=0
add comment to test in sandbox that sometimes fails at given precision, 
current test status: 584 tests  KNOWNFAIL=5, SKIP=40, fail=0

matthew-brett/draft-statsmodels,matthew-brett/draft-statsmodels