Replacing `space.eq_w(...)` by `space.is_true(space.eq(...))` in `compare_arrays` and `index_count_array` in array/ in order to handle NaN correctly

Merged Bitbucket Importer requested to merge branch/array-and-nan into branch/default

Created originally on Bitbucket by Yannick_Jadoul (Yannick Jadoul)

Discovered by trying to fix test_array on py3.7, but noticed the same problem happens on py3.6 and default branches.

Should be merged into 3.6 and 3.7 to get test_array to pass on the py3.7 branch.

See issue #3138 (closed) for more details.

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