Redmine

This patch adds the ability to configure a number of days after which user's passwords should expire. It uses the recently introduced User#passwd_changed_on field. The user-visible end result is the same as if an administrator had manually marked a user with must_changed_passwd.

This patch is against current trunk (r14155) including tests. It was extracted from Planio where we developed this patch for a customer.

This patch might be related to #3155, although this is not directly mentioned there.