RealSchur: change parameter lists; minor rewrite of computeShift().
RealSchur: change parameter lists; minor rewrite of computeShift().

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