make IssuesHelperTest passes when config.threadsafe! is enabled (#12097)

git-svn-id: http://svn.redmine.org/redmine/trunk@12427 e93f8b46-1217-0410-a6f0-8f06a7374b81

lib/redmine.rb

 require 'redmine/activity/fetcher'
 require 'redmine/ciphering'
 require 'redmine/codeset_util'
+require 'redmine/field_format'
 require 'redmine/i18n'
 require 'redmine/menu_manager'
 require 'redmine/notifiable'

test/unit/helpers/issues_helper_test.rb

   include IssuesHelper
   include CustomFieldsHelper
   include ERB::Util
+  include Rails.application.routes.url_helpers
 
   fixtures :projects, :trackers, :issue_statuses, :issues,
            :enumerations, :users, :issue_categories,