revlog: _addrevision creates full-replace deltas based on censored revisions A delta against a censored revision is either received through exchange and written blindly to a revlog, or it is created by the revlog itself. This change ensures the latter process creates deltas which fully replace all data in a censored base using a single patch operation. Recipients of a delta against a censored base will verify that the delta is in this full-replace format. Other recipients will use the delta as normal. For background and broader design of the censorship feature, see: http://mercurial.selenic.com/wiki/CensorPlan