added more third order autodiff tests for:

crossprod, diag_matrix, diag_pre_multiply,diagonal, mdivide_left,
mdivide_left_tri_low, mdivide_right,
mdivide_right_tri_low,multiply_lower_tri_self_transpose_operator_additio
n,operator_division,operator_multiplication,operator_subtraction,tcrossp
rod
added fwd mode tests for sub_row
added fwd mode tests for sub_col