Speed optimization of Z4

Replacement of % 4 with faster & 3

group-connectivity.h

@@ -14,7 +14,7 @@ template < typename T_ > struct Name { \
   static const T zero = 0; \
 }
 
-MakeRing(Z4, 4, (a + b) % 4, (4 - a) % 4, (a * b) % 4, 1);
+MakeRing(Z4, 4, (a + b) & 3, (4 - a) & 3, (a * b) & 3, 1);
 MakeRing(Z2_2, 4, a^b, a, a&b, 3);
 
 }