added migration to add a primary key on nodes id and version - should be run after rake db:node_version

db/migrate/015_add_primary_key_on_nodes_id_version.rb

@@ -0,0 +1,10 @@
+class AddPrimaryKeyOnNodesIdVersion < ActiveRecord::Migration
+
+  #Migration will fail to run unless rake db:node_version has been run previously
+  def self.up
+    add_primary_key "nodes", ["id", "version"] 
+  end
+
+  def self.down
+  end
+end