fixing some tests on ruby 1.9.3

Author: tenderlove

activesupport/lib/active_support/core_ext/date_time/calculations.rb

@@ -81,6 +81,29 @@ def end_of_day
     change(:hour => 23, :min => 59, :sec => 59)
   end
 
+  # 1.9.3 defines + and - on DateTime, < 1.9.3 do not.
+  if DateTime.public_instance_methods(false).include?(:+)
+    def plus_with_duration(other) #:nodoc:
+      if ActiveSupport::Duration === other
+        other.since(self)
+      else
+        plus_without_duration(other)
+      end
+    end
+    alias_method :plus_without_duration, :+
+    alias_method :+, :plus_with_duration
+
+    def minus_with_duration(other) #:nodoc:
+      if ActiveSupport::Duration === other
+        plus_with_duration(-other)
+      else
+        minus_without_duration(other)
+      end
+    end
+    alias_method :minus_without_duration, :-
+    alias_method :-, :minus_with_duration
+  end
+
   # Adjusts DateTime to UTC by adding its offset value; offset is set to 0
   #
   # Example: