Use Py_XDECREF instead of Py_DECREF when the pointer could be null.
Merge pull request #438 from seibert/helper_decref

Fix segfault in _helperlib.c:Numba_recreate_record() caused by incorrect use of Py_DECREF
Fix compilation warnings
Workaround numpy issue (?) under 3.4 in Numba_recreate_record
Merge pull request #439 from pitrou/devel

Workaround numpy issue (?) under 3.4 in Numba_recreate_record
Fix spelling in error message