Patch to allow two-digit years for date and datetime fields

Hi there,

I submitted a patch today to correct an issue I kept running into,
that users would enter in a date of 01/01/90 in a form and 0090-01-01
would be saved to the database. With my patch, Rails will correctly
enter 1990-01-01 into the database.

Ticket is at: http://rails.lighthouseapp.com/projects/8994-ruby-on-rails/tickets/2019-format-two-digit-years-correctly
And the patch itself is: http://rails.lighthouseapp.com/attachments/90772/two_digit_years.diff

This is my first contribution to the Rails core and while I've
followed the contribution guide, I'm anxious to make sure my patch
conforms to whatever most people in Rails expect, so please examine it
critically. Thanks.