add participant_users to conversations

app/models/conversation.rb

@@ -36,11 +36,19 @@ class Conversation < ActiveRecord::Base
   def participant_handles
     self.participants.map{|p| p.diaspora_handle}.join(";")
   end
+  
   def participant_handles= handles
     handles.split(';').each do |handle|
       self.participants << Webfinger.new(handle).fetch
     end
   end
+  
+  def participant_users
+    @participant_users ||= lambda do
+      user_ids = self.participants.map {|p| p.owner_id}.compact
+      User.where(:id => user_ids)
+    end.call
+  end
 
   def last_author
     self.messages.last.author if self.messages.size > 0