Called when a reference to a class is made
@param className
@private
function(className) {
      let t = this;

      // __classes will be null if analyseClasses has not formally been called; this would be if the
      //  analyser is only called externally for getClass()
      if (!t.__classes) {
        t.__classes = []; 
      }

      // Add it
      if (t.__classes.indexOf(className) == -1) {
        t.__classes.push(className); 
      }
    }