it's an easy fix to restore loading calendar.js in head.  unfortunately that adds 84k to initial requests  (prototype is 124k, the html is often ~7-15k range).  so it's a high price for that functionality.  I tried compressing it, and a couple of angles on loading it only when a date editor is requested-- no luck on either score.  there is a general problem here of needing to be able to load cardtype-specific librararies at edit-time.