Rename internal calls to my_mpz* to testobj*

tests/test-mcore.c

@@ -158,8 +158,8 @@ static void test_map(void)
 
 static void test_let(void)
 {
-  M_LET(z, M_CLASSIC_OPLIST(my_mpz)) {
-    my_mpz_add(z,z,z);
+  M_LET(z, M_CLASSIC_OPLIST(testobj)) {
+    testobj_add(z,z,z);
   }
 }