Adds closed_on column that stores the time of the last closing (#824).

The value is preserved when reopening the issue.

git-svn-id: svn+ssh://rubyforge.org/var/svn/redmine/trunk@11402 e93f8b46-1217-0410-a6f0-8f06a7374b81

db/migrate/20130215111127_add_issues_closed_on.rb

@@ -0,0 +1,9 @@
+class AddIssuesClosedOn < ActiveRecord::Migration
+  def up
+    add_column :issues, :closed_on, :datetime, :default => nil
+  end
+
+  def down
+    remove_column :issues, :closed_on
+  end
+end