Fix a couple of issue with the vectorization. In particular, default ei_p* functions

are provided to handle not suported types seemlessly.

Added a generic null-ary expression with null-ary functors. They replace
Zero, Ones, Identity and Random.

Eigen/src/Core/DiagonalCoeffs.h

@@ -54,7 +54,7 @@ struct ei_traits<DiagonalCoeffs<MatrixType> >
     MaxColsAtCompileTime = 1,
     Flags = (RowsAtCompileTime == Dynamic && ColsAtCompileTime == Dynamic
             ? (unsigned int)MatrixType::Flags
-            : (unsigned int)MatrixType::Flags &~ LargeBit) & ~VectorizableBit,
+            : (unsigned int)MatrixType::Flags &~ LargeBit) & ~(VectorizableBit | Like1DArrayBit),
     CoeffReadCost = MatrixType::CoeffReadCost
   };
 };