fix toggling tests

Our ThemeFinder tests left an unclean state. All following tests which accessed a theme (directly or indirectly) failed (sometimes). wierd stuff...

to reproduce this, run the specs with the following options
<pre>
rspec --format documentation --seed 33628 ./spec/controllers/account_controller_spec.rb ./spec/controllers/activities_controller_spec.rb ./spec/controllers/api/v2/authentication_spec.rb ./spec/controllers/api/v2/pagination/principals_controller_spec.rb ./spec/controllers/api/v2/pagination/project_types_controller_spec.rb ./spec/controllers/api/v2/pagination/projects_controller_spec.rb ./spec/controllers/api/v2/pagination/reported_project_statuses_controller_spec.rb ./spec/controllers/api/v2/pagination/statuses_controller_spec.rb ./spec/controllers/api/v2/pagination/types_controller_spec.rb ./spec/controllers/api/v2/pagination/users_controller_spec.rb ./spec/controllers/api/v2/planning_element_journals_controller_spec.rb ./spec/controllers/api/v2/planning_element_priorities_controller_spec.rb ./spec/controllers/api/v2/planning_element_type_colors_controller_spec.rb ./spec/controllers/api/v2/planning_element_types_controller_spec.rb ./spec/controllers/api/v2/planning_elements_controller_spec.rb ./spec/controllers/api/v2/project_associations_controller_spec.rb ./spec/controllers/api/v2/project_types_controller_spec.rb ./spec/controllers/api/v2/projects_controller_spec.rb ./spec/controllers/api/v2/reported_project_statuses_controller_spec.rb ./spec/controllers/api/v2/reportings_controller_spec.rb ./spec/controllers/api/v2/statuses_controller_spec.rb ./spec/controllers/api/v2/timelines_controller_spec.rb ./spec/controllers/api/v2/users_controller_spec.rb ./spec/controllers/api/v2/workflows_controller_spec.rb ./spec/controllers/application_controller_spec.rb ./spec/controllers/attachments_controller_spec.rb ./spec/controllers/auth_sources_controller_spec.rb ./spec/controllers/authentication_spec.rb ./spec/controllers/boards_controller_spec.rb ./spec/controllers/categories_controller_spec.rb ./spec/controllers/copy_projects_controller_spec.rb ./spec/controllers/custom_fields_controller_spec.rb ./spec/controllers/journals_controller_spec.rb ./spec/controllers/ldap_auth_sources_controller_spec.rb ./spec/controllers/members_controller_spec.rb ./spec/controllers/messages_controller_spec.rb ./spec/controllers/my_controller_spec.rb ./spec/controllers/news/comments_controller_spec.rb ./spec/controllers/news_controller_spec.rb ./spec/controllers/planning_element_type_colors_controller_spec.rb ./spec/controllers/project_associations_controller_spec.rb ./spec/controllers/project_types_controller_spec.rb ./spec/controllers/projects_controller_spec.rb ./spec/controllers/query_menu_items_controller_spec.rb ./spec/controllers/reportings_controller_spec.rb ./spec/controllers/repositories_controller_spec.rb ./spec/controllers/search_controller_spec.rb ./spec/controllers/settings_controller_spec.rb ./spec/controllers/statuses_controller_spec.rb ./spec/controllers/timelines_controller_spec.rb ./spec/controllers/timelog_controller_spec.rb ./spec/controllers/users_controller_spec.rb ./spec/controllers/versions_controller_spec.rb ./spec/controllers/wiki_controller_spec.rb ./spec/controllers/wiki_menu_authentication_spec.rb ./spec/controllers/wiki_menu_items_controller_spec.rb ./spec/controllers/work_packages/auto_completes_controller_spec.rb ./spec/controllers/work_packages/bulk_controller_spec.rb ./spec/controllers/work_packages/calendars_controller_spec.rb ./spec/controllers/work_packages/context_menus_controller_spec.rb ./spec/controllers/work_packages/moves_controller_spec.rb ./spec/controllers/work_packages/reports_controller_spec.rb ./spec/controllers/work_packages_controller_spec.rb ./spec/features/accessibility/custom_fields_spec.rb ./spec/features/accessibility/support/toggable_fieldsets_spec.rb ./spec/features/accessibility/work_packages/index_toggable_fieldsets_spec.rb ./spec/features/accessibility/work_packages/work_package_query_spec.rb ./spec/features/categories/delete_spec.rb ./spec/features/projects/delete_projects_spec.rb ./spec/features/work_packages/select_query_spec.rb ./spec/features/workflows/copy_spec.rb ./spec/helpers/application_helper_spec.rb ./spec/helpers/avatar_helper_spec.rb ./spec/helpers/pagination_helper_spec.rb ./spec/helpers/projects_helper_spec.rb ./spec/helpers/search_helper_spec.rb ./spec/helpers/users_helper_spec.rb ./spec/helpers/work_packages_helper_spec.rb ./spec/lib/acts_as_journalized/journaled_spec.rb ./spec/lib/acts_as_list/acts_as_list_patch_spec.rb ./spec/lib/acts_as_watchable/lib/acts_as_watchable/routes_spec.rb ./spec/lib/copy_model/copy_model_spec.rb ./spec/lib/journal_formatter/attachment_spec.rb ./spec/lib/journal_formatter/custom_field_spec.rb ./spec/lib/journal_formatter/diff_spec.rb ./spec/lib/open_project/configuration_spec.rb ./spec/lib/open_project/footer_spec.rb ./spec/lib/open_project/passwords_spec.rb ./spec/lib/open_project/themes/default_theme_spec.rb ./spec/lib/open_project/themes/theme_finder_spec.rb ./spec/lib/open_project/themes/theme_spec.rb ./spec/lib/open_project/themes/view_helpers_spec.rb ./spec/lib/open_project/themes_spec.rb ./spec/lib/redcloth/redcloth_spec.rb ./spec/lib/redmine/i18n_spec.rb ./spec/mailers/user_mailer_spec.rb ./spec/models/activity/work_package_activity_provider_spec.rb ./spec/models/available_project_status_spec.rb ./spec/models/custom_field_spec.rb ./spec/models/deleted_user_spec.rb ./spec/models/group_spec.rb ./spec/models/journal_manager_spec.rb ./spec/models/mail_handler_spec.rb ./spec/models/member_spec.rb ./spec/models/menu_item_spec.rb ./spec/models/menu_items/query_menu_item_spec.rb ./spec/models/menu_items/wiki_menu_item_spec.rb ./spec/models/news_spec.rb ./spec/models/permitted_params_spec.rb ./spec/models/planning_element_type_color_spec.rb ./spec/models/principal_spec.rb ./spec/models/project/copy_spec.rb ./spec/models/project_association_spec.rb ./spec/models/project_spec.rb ./spec/models/project_type_spec.rb ./spec/models/queries/work_packages/filter_spec.rb ./spec/models/query/results_spec.rb ./spec/models/query_spec.rb ./spec/models/reported_project_status_spec.rb ./spec/models/reporting_spec.rb ./spec/models/reports_services_spec.rb ./spec/models/role_spec.rb ./spec/models/system_user_spec.rb ./spec/models/timeline_spec.rb ./spec/models/timelines_project_spec.rb ./spec/models/user_deletion_spec.rb ./spec/models/user_password_spec.rb ./spec/models/user_spec.rb ./spec/models/version_spec.rb ./spec/models/watcher_spec.rb ./spec/models/wiki_page_spec.rb ./spec/models/wiki_spec.rb ./spec/models/work_package/ask_before_destruction_spec.rb ./spec/models/work_package/planning_comparison_spec.rb ./spec/models/work_package/work_package_action_mailer_spec.rb ./spec/models/work_package/work_package_acts_as_event_spec.rb ./spec/models/work_package/work_package_acts_as_journalized_spec.rb ./spec/models/work_package/work_package_acts_as_searchable_spec.rb ./spec/models/work_package/work_package_acts_as_watchable_spec.rb ./spec/models/work_package/work_package_copy_spec.rb ./spec/models/work_package/work_package_custom_fields_spec.rb ./spec/models/work_package/work_package_nested_set_spec.rb ./spec/models/work_package/work_package_planning_spec.rb ./spec/models/work_package/work_package_relations_spec.rb ./spec/models/work_package/work_package_reschedule_after_spec.rb ./spec/models/work_package/work_package_scheduling_spec.rb ./spec/models/work_package/work_package_status_spec.rb ./spec/models/work_package/work_package_validations_spec.rb ./spec/models/work_package/work_package_visibility_spec.rb ./spec/models/work_package_spec.rb ./spec/permissions/add_work_packages_spec.rb ./spec/permissions/copy_projects_spec.rb ./spec/permissions/delete_work_packages_spec.rb ./spec/permissions/edit_journals_spec.rb ./spec/permissions/edit_work_packages_spec.rb ./spec/permissions/export_work_packages_spec.rb ./spec/permissions/manage_boards_spec.rb ./spec/permissions/view_work_packages_spec.rb ./spec/permissions/work_packages_bulk_spec.rb ./spec/requests/auth/api_v2_spec.rb ./spec/requests/old_issue_2_wp_spec.rb ./spec/routing/api/v2/pagination_spec.rb ./spec/routing/api/v2/planning_element_priorities_routing_spec.rb ./spec/routing/api/v2/workflows_spec.rb ./spec/routing/boards_routing_spec.rb ./spec/routing/categories_spec.rb ./spec/routing/journals_spec.rb ./spec/routing/project_routing_spec.rb ./spec/routing/repositories_routing_spec.rb ./spec/routing/search_spec.rb ./spec/routing/status_routing_spec.rb ./spec/routing/timelog_spec.rb ./spec/routing/users_routing_spec.rb ./spec/routing/watchers_spec.rb ./spec/routing/wiki_routing_spec.rb ./spec/routing/work_package/auto_completes_routing_spec.rb ./spec/routing/work_package/calendars_routing_spec.rb ./spec/routing/work_package/context_menus_routing_spec.rb ./spec/routing/work_package/previews_routing_spec.rb ./spec/routing/work_package/reports_routing_spec.rb ./spec/routing/work_package_bulk_spec.rb ./spec/routing/work_packages_spec.rb ./spec/views/api/v1/issues/index_api_rsb_spec.rb ./spec/views/api/v1/issues/show_api_rsb_spec.rb ./spec/views/api/v2/authentication/index_api_json_spec.rb ./spec/views/api/v2/authentication/index_api_xml_spec.rb ./spec/views/api/v2/custom_fields/index_api_rabl_spec.rb ./spec/views/api/v2/planning_element_priorities/index_api_xml_spec.rb ./spec/views/api/v2/planning_element_type_colors/index_api_json_spec.rb ./spec/views/api/v2/planning_element_type_colors/show_api_json_spec.rb ./spec/views/api/v2/planning_element_types/index_api_json_spec.rb ./spec/views/api/v2/planning_element_types/show_api_json_spec.rb ./spec/views/api/v2/planning_elements/destroy_api_json_spec.rb ./spec/views/api/v2/planning_elements/index_api_json_spec.rb ./spec/views/api/v2/planning_elements/index_api_xml_spec.rb ./spec/views/api/v2/planning_elements/show_api_json_spec.rb ./spec/views/api/v2/project_associations/available_projects_api_json_spec.rb ./spec/views/api/v2/project_associations/index_api_json_spec.rb ./spec/views/api/v2/project_associations/show_api_json_spec.rb ./spec/views/api/v2/project_types/index_api_json_spec.rb ./spec/views/api/v2/project_types/show_api_json_spec.rb ./spec/views/api/v2/projects/index_api_json_spec.rb ./spec/views/api/v2/projects/show_api_json_spec.rb ./spec/views/api/v2/projects/show_api_xml_spec.rb ./spec/views/api/v2/reported_project_statuses/index_api_json_spec.rb ./spec/views/api/v2/reported_project_statuses/show_api_json_spec.rb ./spec/views/api/v2/reportings/index_api_json_spec.rb ./spec/views/api/v2/reportings/show_api_json_spec.rb ./spec/views/api/v2/statuses/index_api_json_spec.rb ./spec/views/api/v2/statuses/show_api_json_spec.rb ./spec/views/api/v2/users/index_api_json_spec.rb ./spec/views/api/v2/workflows/index_api_xml_spec.rb ./spec/views/my/page.html.erb_spec.rb ./spec/views/repositories/stats.html.erb_spec.rb ./spec/views/users/show.html.erb_spec.rb ./spec/views/wiki/new.html.erb_spec.rb ./spec/views/work_package/auto_complete/index_spec.rb ./spec/views/work_package/show.html.erb_spec.rb
</pre>