move logic to use latest image file attachment to class method for common use (#3261)

git-svn-id: svn+ssh://rubyforge.org/var/svn/redmine/trunk@7908 e93f8b46-1217-0410-a6f0-8f06a7374b81

app/models/attachment.rb

@@ -167,6 +167,12 @@ class Attachment < ActiveRecord::Base
     {:files => attached, :unsaved => obj.unsaved_attachments}
   end
 
+  def self.latest_attach(attachments, filename)
+    attachments.sort_by(&:created_on).reverse.detect { 
+      |att| att.filename.downcase == filename.downcase
+     }
+  end
+
 private
   def sanitize_filename(value)
     # get only the filename, not the whole path