Move the Base typedef's from private to public scope
Move the Base typedef's from private to public scope

Move the Quaternion::Base typedef from private to public scope so that one may
create child classes of Quaternion.

NOTE: This matches the semantics of MatrixBase.

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