Fix Bug 507: Mark variable as unused in NDEBUG case
Fix Bug 507: Mark variable as unused in NDEBUG case

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