Allow messages to be deleted from the outbox as well as the inbox.

db/migrate/037_add_sender_visible_to_message.rb

@@ -0,0 +1,11 @@
+class AddSenderVisibleToMessage < ActiveRecord::Migration
+  def self.up
+    rename_column :messages, :visible, :to_user_visible
+    add_column :messages, :from_user_visible, :boolean, :default => true, :null => false
+  end
+
+  def self.down
+    remove_column :messages, :from_user_visible
+    rename_column :messages, :to_user_visible, :visible
+  end
+end