Possible performance regression in a1fee9

Possible performance regression in https://github.com/pandas-dev/pandas/commit/a1fee9199eba7ebf423880243936b9f1501d3d3a.

Regression: http://pandas.pydata.org/speed/pandas/index.html#rolling.Quantile.time_quantile?commits=a1fee9199eba7ebf423880243936b9f1501d3d3a&p-window=1000&p-param5=%27lower%27&p-percentile=0.5&p-dtype=%27float%27&p-constructor=%27DataFrame%27
Benchmark: 15.23% rolling.Quantile.time_quantile('DataFrame', 1000, 'float', 0.5, 'lower')

cc @BryanCutler.