Allow the filter to filter by date only (not time) irrespective of granularity setting.

Hi.
For my application I need the ability to filter dates by a specific date, even though they need to be shown etc with minute granularity.

I couldn't find a way to do this in the standard 5.x-2.3 so I made this patch to add an extra filter for each CCK date field that matches just a date, rather than a date/time.

I don't know if anyone else is even vaguely interested in it, but it'd really help me if someone could cast an eye over it and let me know if I've done the right thing or not. It'd be even more convenient if it made it into the date module itself, then I wouldn't need to re-write and apply the patch on every update ;)