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/util/Constants.h

@@ -38,6 +38,7 @@ const unsigned int VectorizableBit = 0x10;
 #else
 const unsigned int VectorizableBit = 0x0;
 #endif
+const unsigned int Like1DArrayBit = 0x20;
 
 enum { ConditionalJumpCost = 5 };
 enum CornerType { TopLeft, TopRight, BottomLeft, BottomRight };