[eigen] VectorBase issue

["Gael Guennebaud" <gael.guennebaud@xxxxxxxxx>]

Hi list,

In order to properly discard vector specific features to the rest of the API I tried to add a  templated VecorBase base class from which MatrixBase would automatically inherit if the _expression_ is indeed a vector:

template<typename Derived> class MatrixBase
: public VectorBase<Derived> { /*common API*/ };

template<typename Derived, 
              bool IsVector=Derived:IsVector> class VectorBase { /*empty*/ };