add operator+ scalar to AutoDiffScalar
add operator+ scalar to AutoDiffScalar

mjbshaw/Eigen,rotorliu/eigen,mjbshaw/Eigen,madlib/eigen_backup,madlib/eigen_backup,madlib/eigen_backup,rotorliu/eigen,rotorliu/eigen,mjbshaw/Eigen,mjbshaw/Eigen,madlib/eigen_backup,rotorliu/eigen