Improve test suite.

tests/test-mcore.c

@@ -270,6 +270,10 @@ static void test_reduce(void)
 #define add(a,b) a + b
   assert ( M_REDUCE2(id, add, d, M_SEQ(1, 5)) == 5 * 6 /2);
   assert ( M_REDUCE2(id, add, d, M_SEQ(1, 10)) == 10 * 11 /2);
+
+  assert ( M_REDUCE(M_ID, add, M_SEQ(1, 5))
+           + M_REDUCE(M_ID, add, M_SEQ(6, 10))
+           == M_REDUCE(M_ID, add, M_SEQ(1, 10)));                    
 }
 
 int main(void)