* 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/CwiseBinaryOp.h

@@ -66,7 +66,7 @@ struct ei_traits<CwiseBinaryOp<BinaryOp, Lhs, Rhs> > : ei_traits<Lhs>
     LhsFlags = _LhsNested::Flags,
     RhsFlags = _RhsNested::Flags,
     StorageOrdersAgree = (int(Lhs::Flags)&RowMajorBit)==(int(Rhs::Flags)&RowMajorBit),
-    Flags = (int(LhsFlags) | int(RhsFlags)) & (
+    Flags0 = (int(LhsFlags) | int(RhsFlags)) & (
         HereditaryBits
       | (int(LhsFlags) & int(RhsFlags) &
            ( AlignedBit
@@ -75,6 +75,7 @@ struct ei_traits<CwiseBinaryOp<BinaryOp, Lhs, Rhs> > : ei_traits<Lhs>
            )
         )
      ),
+    Flags = (Flags0 & ~RowMajorBit) | (LhsFlags & RowMajorBit),
     CoeffReadCost = LhsCoeffReadCost + RhsCoeffReadCost + ei_functor_traits<BinaryOp>::Cost
   };
 };