Merge branch 'handle-appearance-upgrade-ce-to-ee' into 'master'

Handle duplicate appearances table creation issue with upgrade from CE to EE

Closes #391

See merge request !278

CHANGELOG-EE

 Please view this file on the master branch, on stable branches it's out of date.
 
 v 8.6.0 (unreleased)
+  - Handle duplicate appearances table creation issue with upgrade from CE to EE
   - Improve weight filter for issues
   - Clear "stuck" mirror updates before periodically updating all mirrors.
   - [Elastic] Add elastic checker to gitlab:check

db/migrate/20140414093351_create_appearances.rb

 class CreateAppearances < ActiveRecord::Migration
   def change
+    # GitLab CE may already have created this table, so to preserve
+    # the upgrade path from CE -> EE we only create this if necessary.
+    unless table_exists?(:appearances)
       create_table :appearances do |t|
         t.string :title
         t.text :description
@@ -9,4 +12,5 @@ class CreateAppearances < ActiveRecord::Migration
         t.timestamps
       end
     end
+  end
 end