code: @Override public void init(boolean expensive) {
      super.init(expensive);
      if( _parms._max_iterations < 1 || _parms._max_iterations > 9999999 )
        error("max_iterations", "must be between 1 and 10 million");
    }
docs: Initialize the ModelBuilder, validating all arguments and preparing the
  training frame.  This call is expected to be overridden in the subclasses
  and each subclass will start with "super.init();".  This call is made
  by the front-end whenever the GUI is clicked, and needs to be fast;
  heavy-weight prep needs to wait for the trainModel() call.
  
  Validate the max_iterations.