moving op_*_vari's out of stan/agrad/agrad.hpp
moving op_*_vari's out of stan/agrad/agrad.hpp

stan-dev/math,stan-dev/math,stan-dev/math,stan-dev/stan,stan-dev/stan,stan-dev/math,stan-dev/stan,stan-dev/math,stan-dev/math,stan-dev/stan,stan-dev/stan,stan-dev/math,stan-dev/math,stan-dev/math