Change auto update period for membership renewals

If you have a $2/month membership dues and a member renews with $12 at once, it would be useful to be able to indicate that the membership end date should be extended by 6 months rather than the default 1 month.

The solution could be: Add a text line in the UI that says: Extend membership end date by 1 term, with a link next to it that says "change" which would transform it into a text field in which the user could add an arbitrary number.

See discussion:

http://forum.civicrm.org/index.php/topic,20715.0.html