code: function traceModule (moduleName, context, processHook)
    {
      var module = context.modules[moduleName];
      if (!module)
        fatal ('Module <cyan>%</cyan> was not found.', moduleName);
      // Ignore the module if it's external.
      if (module.external)
        return;
      // Include required submodules first.
      context.trigger (ContextEvent.ON_BEFORE_DEPS, [module]);
      module.requires.forEach (function (modName)
      {
        traceModule (modName, context, processHook);
      });
      // Ignore references to already loaded modules or to explicitly excluded modules.
      if (!context.loaded[module.name] && !~context.options.excludedModules.indexOf (module.name)) {
        info ('Including module <cyan>%</cyan>.', moduleName);
        context.loaded[module.name] = true;
        processHook (module);
      }
    }
docs: Traces a dependency graph for the specified module and calls the given callback
  to process each required module in the correct loading order.
  @param {string} moduleName
  @param {Context} context The execution context for the middleware stack.
  @param {function(ModuleDef)} processHook