CLN: Specialize assert_(np.array_equal(...))
Work on #6175. Work in progress. One more commit needed to finish; splitting to keep reasonably sized.
- Changes assert_numpy_array_equals to assert_numpy_array_equal, for consistency with other methods. (API change of recently-added function)
- Changes instances of assert_(np.array_equal(A,B)) to assert_numpy_array_equal(A,B)
- Update release.rst to reflect work on #6175

The proposed API change affects a function @KTAtkinson added this week. I changed all instances in master.

Tests still pass locally.
 pls rebase on master - lots of recent changes 
 @jreback: should be all set.
 @bwignall thanks again!
