Fix #555: test failures under Windows (or possibly other 32-bit platforms) on math.trunc tests
Refactor mathimpl a bit and add docstrings
Merge branch 'master' of github.com:numba/numba into trunc_int_return_width
Merge pull request #556 from pitrou/trunc_int_return_width

Fix #555: test failures under Windows (or possibly other 32-bit platforms) on math.trunc tests