Consolidate functionality shared between Issue and MergeRequest

Any associations, validations, delegates, scopes and methods that
were exactly the same in both Issue and MergeRequest models have been
moved to a new IssueCommonality module (role) that gets included by each
class.

There was actually quite a bit of duplication, because MergeRequests are
basically just specialized Issues.

app/roles/issue_commonality.rb

@@ -1,3 +1,50 @@
 # Contains common functionality shared between Issues and MergeRequests
 module IssueCommonality
+  extend ActiveSupport::Concern
+
+  included do
+    attr_protected :author, :author_id, :project, :project_id
+
+    belongs_to :project
+    belongs_to :author, :class_name => "User"
+    belongs_to :assignee, :class_name => "User"
+    has_many :notes, :as => :noteable, :dependent => :destroy
+
+    validates_presence_of :project_id
+    validates_presence_of :author_id
+
+    validates :title,
+              :presence => true,
+              :length   => { :within => 0..255 }
+
+
+    scope :opened, where(:closed => false)
+    scope :closed, where(:closed => true)
+    scope :assigned, lambda { |u| where(:assignee_id => u.id)}
+
+    delegate :name,
+             :email,
+             :to => :author,
+             :prefix => true
+
+    delegate :name,
+             :email,
+             :to => :assignee,
+             :allow_nil => true,
+             :prefix => true
+
+    attr_accessor :author_id_of_changes
+  end
+
+  def self.search query
+    where("title like :query", :query => "%#{query}%")
+  end
+
+  def today?
+    Date.today == created_at.to_date
+  end
+
+  def new?
+    today? && created_at == updated_at
+  end
 end