The `--help`/`-h` option doesn't work

[aik099]

The --help/-h option processing works like this:

1. the Application has private wantHelps property
2. when the --help/-h option is given, then the wantHelps property is set to true
3. when Application::get is used to retrieve a command, then a HelpCommand is retrieved instead
4. the first code to call Application::get is the one, that executes the command, that the user requested
   .

However, the AggregateCommand::setApplication method requests all commands but doesn't execute all of them causing the wantHelps property to reset and no help screen is shown.