Multibinder should accept bindings to sets of elements

[GoogleCodeExporter]

Multibinder should accept bindings to sets whose size is not known until 
injector creation and then add all the elements of the sets to the multibound 
set.  Contrived example:

Multibinder.newSetBinder(binder(), User.class, MyAnnotation.class)
  .addSetBinding().toProvider(HappyEngineersProvider.class);

class HappyEngineersProvider implements Provider<Set<User>> {
  @Inject Company company;

  @Override public Set<User> get() {
    Set<User> happyEngineers = new HashSet<User>();
    for (User e : company.getEngineers())
      if (e.isHappy())
        happyEngineers.add(e);
    return happyEngineers;
  }
}

Original issue reported on code.google.com by mattmccu...@google.com on 21 Oct 2011 at 9:12