Override MatrixBase::eval() since matrices don't need to be evaluated, it is enough to just read them.
Override MatrixBase::eval() since matrices don't need
to be evaluated, it is enough to just read them.

--HG--
extra : convert_revision : svn%3A283d02a7-25f6-0310-bc7c-ecb5cbfe19da/branches/work/eigen2%40822542

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