TST: clean up ndimage.measurements tests for docstrings.
TST: silence ndimage test warnings coming from ``np.mean([])``.
TST: silence deprecation warnings for optimize.anneal in test suite.
TST: fix fragile test for stats.itemfreq.  Was failing with numpy master.
Merge pull request #3223 from rgommers/ndimage-warnings

TST: fix test errors with numpy master