Ruby 1.9: fix Time#beginning_of_day inaccuracy due to subtracting a Float

Author: jeremy

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

@@ -201,7 +201,8 @@ def next_week(day = :monday)
 
         # Returns a new Time representing the start of the day (0:00)
         def beginning_of_day
-          (self - self.seconds_since_midnight).change(:usec => 0)
+          #(self - seconds_since_midnight).change(:usec => 0)
+          change(:hour => 0, :min => 0, :sec => 0, :usec => 0)
         end
         alias :midnight :beginning_of_day
         alias :at_midnight :beginning_of_day