BUG: np.ma.compress treated inputs in wrong order; closes #2495
BUG: add __len__ method to ma.mvoid; closes #576
Merge pull request #3447 from efiring/ma_mvoid_len

BUG: add __len__ method to ma.mvoid; closes #576
Merge pull request #3448 from efiring/ma_compress

BUG: np.ma.compress treated inputs in wrong order; closes #2495