BUG: Catch DeprecationWarning in numpy/core/tests/test_numeric.py.

TestCreationFuncs.check_function was spewing Deprecation warnings in
release mode. AFAICT, it did not raise errors during development because
it was buried by a TypeError. The Deprecation in question is at line
1141 in multiarray/conversion_utils.c. Hiding the deprecation should
be harmless here, but when the Deprecation is turned into an error
it will need to be caught in the test.
MAINT: Make Warning handling cleaner in test_concatenate_sloppy0.

The test in question is in numpy/core/tests/test_shape_base. The cleanup
consists of using warning.catch_warnings instead of setting and popping the
warnings filter.
BUG: Make DeprecationWarning always raise error in test.

The test_fancy in numpy/lib/tests/test_function_base.py failed in
release because a DeprecationWarning was no longer raised, it had
become a warning.
Merge pull request #3670 from charris/backport-test-fixes

Backport test fixes