Merge branch 'activity_publicly_accessible' into 'master'

Public project activity page asks for sign-in

https://gitlab.com/gitlab-org/gitlab-ce/issues/2021

See merge request !1007

app/controllers/projects_controller.rb

 class ProjectsController < ApplicationController
   prepend_before_filter :render_go_import, only: [:show]
-  skip_before_action :authenticate_user!, only: [:show]
+  skip_before_action :authenticate_user!, only: [:show, :activity]
   before_action :project, except: [:new, :create]
   before_action :repository, except: [:new, :create]