Allow template deduction for partially specified types.
Allow template deduction for partially specified types.

This fully resolves #1542.

cython/cython,ChristopherHogan/cython,cython/cython,da-woods/cython,fabianrost84/cython,cython/cython,da-woods/cython,cython/cython,scoder/cython,scoder/cython,fabianrost84/cython,scoder/cython,da-woods/cython,ChristopherHogan/cython,fabianrost84/cython,scoder/cython,fabianrost84/cython,ChristopherHogan/cython,da-woods/cython,fabianrost84/cython