Impossible to manually the date in an input

In Firefox and Chrome – I didn't test with other browsers –, user cannot manually edit the date in the text field. Every-time a key is pressed, the date is parsed, and the content of the text field is overridden.

For example, if I want to enter `1/1/2012`: I type `1`, and by the time I type `/`, the content of the text field is replaced with `01/01/0000`.

Here's my proposed fix.

Feel free to comment/criticize my fix.