Update tests for new abs semantics.
Update tests for new abs semantics.

See discussion at https://github.com/cython/cython/issues/1837

cython/cython,da-woods/cython,scoder/cython,da-woods/cython,cython/cython,scoder/cython,cython/cython,cython/cython,da-woods/cython,da-woods/cython,scoder/cython,scoder/cython