fix BTL's eigen interface (transplanted from 942fa62f37308f9738c57c520bd7ce8d55b024bf)
fix BTL's eigen interface
(transplanted from 942fa62f37308f9738c57c520bd7ce8d55b024bf)

--HG--
extra : transplant_source : %94/%A6/70%8F%978%C5%7CR%0B%D7%CE%8DU%B0%24%BF

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