added model Comment.

comments can now be added on news.

git-svn-id: http://redmine.rubyforge.org/svn/trunk@81 e93f8b46-1217-0410-a6f0-8f06a7374b81

app/models/comment.rb

@@ -0,0 +1,6 @@
+class Comment < ActiveRecord::Base
+  belongs_to :commented, :polymorphic => true, :counter_cache => true
+  belongs_to :author, :class_name => 'User', :foreign_key => 'author_id'
+
+  validates_presence_of :commented, :author, :comment
+end