Retain compatibility with RSpec 2 matchers

lib/paranoia/rspec.rb

@@ -6,4 +6,8 @@ RSpec::Matchers.define :act_as_paranoid do
 
   failure_message { "expected #{subject.class} to use `acts_as_paranoid`" }
   failure_message_when_negated { "expected #{subject.class} not to use `acts_as_paranoid`" }
+
+  # RSpec 2 compatibility:
+  alias_method :failure_message_for_should, :failure_message
+  alias_method :failure_message_for_should_not, :failure_message_when_negated
 end