Fixed match method.

isEntailed returns the wrong value. For example:

```java
public static void main(String[] args) {
    Solver s = new Solver();
    IntVar three = VF.fixed(3, s);
    IntVar two = VF.fixed(2, s);
    s.post(ICF.arithm(three, "-", two, "=", 1));
    System.out.println(s.findSolution());
    System.out.println(s.isEntailed());
}
```

Prints "true \n false". It should print "true \n true".