Show merge requests which close current issue Closes #2903 ### What does this MR do If an issue is to be closed by a merge request the current user has access to, this will be displayed when the user looks at the issue. ![Screenshot_from_2015-10-12_12-10-37](https://gitlab.com/zj/gitlab-ce/uploads/52e429704e73067b24b69801f13ad7bc/Screenshot_from_2015-10-12_12-10-37.png) /cc @DouweM See merge request !1569