added more test for columns_dot_product in fvar/matrix
added more test for columns_dot_product in fvar/matrix

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