Price Fields with time interval. Useful for early bird and late registrations, temporary discounts, etc.

This feature provides for price fields that are available only during time intervals. The price field is shown only If the current time falls between the activation and expiration times. Useful for early bird and late registrations, temporary discounts, etc.

This patch includes the missing filtering logic and makes a few changes here and there to deal with the interface details.

Please refer to http://forum.civicrm.org/index.php/topic,11926.0.html