Fix doc'n of FullPivLU re permutation matrices (bug 815).
Fix doc'n of FullPivLU re permutation matrices (bug 815).

--HG--
extra : transplant_source : d%BE%86Y%F6%06%97%02%11%EF%83%F1.%BD%40%16H%C9h%5C

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