fix that project auto generation fails when projects created in the same time (#14242)

git-svn-id: svn+ssh://rubyforge.org/var/svn/redmine/trunk@11942 e93f8b46-1217-0410-a6f0-8f06a7374b81

app/models/project.rb

@@ -688,7 +688,7 @@ class Project < ActiveRecord::Base
 
   # Returns an auto-generated project identifier based on the last identifier used
   def self.next_identifier
-    p = Project.order('created_on DESC').first
+    p = Project.order('id DESC').first
     p.nil? ? nil : p.identifier.to_s.succ
   end