Fix test case message in multitest checkers with partial scores

[nsychev]

Usually when we have multitest problems and support partial scores, checkers look like that:

int points = 0;
for (int i = 1; i <= t; i++) {
  setTestCase(i);
  // check test case i
  points += testPoints; // (or std::min here)
}
quitp(points);

Now testlib prints message points 12345 (test case 100) which differs from quitf(_ok): ok (100 test cases). I think similar behavior should be implemented in both cases.