Fix test_copyreg when numpy is installed: test.pickletester now
saves/restores warnings.filters when importing numpy, to ignore
filters installed by numpy.
Add the save_restore_warnings_filters() function to the
test.support.warnings_helper module.
distutils.tests now saves/restores warnings filters to leave them
unchanged. Importing tests imports docutils which imports
pkg_resources which adds a warnings filter.
Victor Stinner
Éric Araujo
Fred Drake