* allow matrix dimensions to be 0 (also at compile time) and provide a specialization

of ei_matrix_array for size 0
* adapt many xprs to have the right storage order, now that it matters
* add static assert on expressions to check that vector xprs
  have the righ storage order
* adapt ei_plain_matrix_type_(column|row)_major
* implement assignment of selfadjointview to matrix
  (was before failing to compile) and add nestedExpression() methods
* expand product_symm test
* in ei_gemv_selector, use the PlainObject type instead of a custom Matrix<...> type
* fix VectorBlock and Block mistakes

Eigen/src/Core/SelfAdjointView.h

@@ -99,6 +99,9 @@ template<typename MatrixType, unsigned int UpLo> class SelfAdjointView
     /** \internal */
     const MatrixType& _expression() const { return m_matrix; }
 
+    const MatrixType& nestedExpression() const { return m_matrix; }
+    MatrixType& nestedExpression() { return const_cast<MatrixType&>(m_matrix); }
+
     /** Efficient self-adjoint matrix times vector/matrix product */
     template<typename OtherDerived>
     SelfadjointProductMatrix<MatrixType,Mode,false,OtherDerived,0,OtherDerived::IsVectorAtCompileTime>