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

test/fixtures/issues.yml

@@ -152,6 +152,7 @@ issues_008:
   root_id: 8
   lft: 1
   rgt: 2
+  closed_on: <%= 3.days.ago.to_s(:db) %>
 issues_009: 
   created_on: <%= 1.minute.ago.to_s(:db) %>
   project_id: 5
@@ -209,6 +210,7 @@ issues_011:
   root_id: 11
   lft: 1
   rgt: 2
+  closed_on: <%= 1.day.ago.to_s(:db) %>
 issues_012: 
   created_on: <%= 3.days.ago.to_s(:db) %>
   project_id: 1
@@ -228,6 +230,7 @@ issues_012:
   root_id: 12
   lft: 1
   rgt: 2
+  closed_on: <%= 1.day.ago.to_s(:db) %>
 issues_013:
   created_on: <%= 5.days.ago.to_s(:db) %>
   project_id: 3