Patch by Gael Guennebaud: coeff-wise binary operators.

This unifies + and - and moreover this patch introduces
coeff-wise * and / based on this. Also, corresponding test.

test/main.h

@@ -121,6 +121,7 @@ class EigenTest : public QObject
     void testMiscMatrices();
     void testSmallVectors();
     void testMap();
+    void testCwiseops();
   protected:
     int m_repeat;
 };