BUG: Bug in fillna with method = bfill/ffill and datetime64[ns] dtype (GH6587)
Merge pull request #6588 from jreback/date_fill

BUG: Bug in fillna with method = bfill/ffill and datetime64[ns] dtype (GH6587)
EHN/FIX: Add na_position parameter to DataFrame.sort. Fixes GH3917

TST: Skip mergesort test if `np.argsort` raises TypeError on any mergesort.