ActiveSupport、Date#to_time

>> require "rubygems"
=> true
>> require "active_support"
=> true
>> Date.new(2008,12,31).to_time => Wed Dec 31 00:00:00 +0900 2008
>> Date.new(2008,12,31).to_time.class
=> Time
>> Date.new(2008,12,31).to_time(:utc)
=> Wed Dec 31 00:00:00 UTC 2008