[2.0.0-RC5] distinctUntilChanged doesn't work nicely with mutable objects

[nsk-mironov]

public class Main {
  static class Header {
    String name = "key";
    String value = "one";
  }

  public static void main(String[] args) {
    final Header header = new Header();
    final BehaviorSubject<Header> subject = BehaviorSubject.createDefault(header);

    subject.distinctUntilChanged(new Function<Header, Object>() {
      @Override
      public Object apply(final Header header) throws Exception {
        return header.value;
      }
    }).subscribe(new Consumer<Header>() {
      @Override
      public void accept(final Header header) throws Exception {
        System.out.println("Name = " + header.name + ", Value = " + header.value);
      }
    });

    header.value = "two";
    subject.onNext(header);
  }
}

Output:

Name = key, Value = one

Expected output:

Name = key, Value = one
Name = key, Value = two

The same code used to work as expected with 2.0.0-RC4 and all previous RxJava versions.

[akarnokd]

Fixed via #4747