Add size checks to elt_divide and elt_multiply
Add size checks to elt_divide and elt_multiply

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