Set of functions used in the tests.
Migrating to use tests_support.
Updating 2D_latlon tests to use tests_support.
Bugfix on input types of cython's wmean_2D_latlon.
Renaming eval_ones -> eval_ones_2D
New cython's wmean_2D_latlon under way. Unfinished.

Works fine for ndarray, and masked array with only valid values.
Better nomenclature @ apply_window_mean_2Dn_latlon.

Using n, and keeping i and j indexes like @ apply_window_mean_2D_latlon
to keep consistency and avoid confusion and easier to bugtrack.
test_mask_at_interp now uses tests_support.
test_Python_x_Cython also test on masked array.