Merge branch 'bugfix/jschatz1/issuable-consistency' into 'master'

Consistency in MR and issue header.

Fixes: #13550 

![Screen_Shot_2016-02-18_at_11.20.19_AM](/uploads/8327ff045e45029b85b2cbac72c98a7f/Screen_Shot_2016-02-18_at_11.20.19_AM.png)![Screen_Shot_2016-02-18_at_11.20.55_AM](/uploads/f79613ebb23e4a62fb1bdb48d6f7fd2b/Screen_Shot_2016-02-18_at_11.20.55_AM.png)

See merge request !2874

app/views/projects/merge_requests/show/_mr_title.html.haml

@@ -5,7 +5,7 @@
     Merge Request ##{@merge_request.iid}
   %span.creator
     ·
-    opened by #{link_to_member(@project, @merge_request.author, size: 24)}
+    by #{link_to_member(@project, @merge_request.author, size: 24)}
     ·
     = time_ago_with_tooltip(@merge_request.created_at)