Don't work with Date about date_validator

[txus]

Sorry, I couldn't apply your pull request because it breaks a spec (the one checking the :after_or_equal_to clause).
Turns out that somehow comparing two equal datetimes or times with >= (but not with <=) returns false. I've been researching but the best solution I found a couple days ago was to convert them to integer before comparing them; now I've fixed that Date thing converting all TimeWithZones and Dates to datetime before the to_i, so there should be no problem now.
Let me know if you find out about that datetime comparison strange issue, maybe it's my ruby version or I don't know! And thank you for contributing ;)

[naumov]

Thanks for so quick fix! :)

But there is small issue in your fix, too. It is when you do value = value.to_datetime and then pass record.errors.add(... :value => value ...). The original value is a Date, but the one is passed to i18n error message is an Datetime(becouse you convert the value directly). This couse a small issue with formatting in error messages.

I think it is better to introduce a new variable for comparison, but pass the original one to i18n error.

[txus]

Yep! fixed. However I'm thinking this actually means that the i18n part is not covered by tests, so I think maybe tomorrow I'm giving it a try and get it covered to avoid future bugs!