Fix bug 613: psqrt was incorrect for small numbers
Fix bug 613: psqrt was incorrect for small numbers

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