preserve database integrity for recurring todos when deleting project or context. Fixes #880. Fixes #895

app/models/project.rb

@@ -1,6 +1,7 @@
 class Project < ActiveRecord::Base
   has_many :todos, :dependent => :delete_all, :include => :context
   has_many :notes, :dependent => :delete_all, :order => "created_at DESC"
+  has_many :recurring_todos
   belongs_to :default_context, :class_name => "Context", :foreign_key => "default_context_id"
   belongs_to :user