revlog: fix for generaldelta distance calculation The decision whether or not to store a full snapshot instead of a delta is done based on the distance value calculated in _addrevision.builddelta(rev). This calculation traditionally used the fact of deltas only using the previous revision as base. Generaldelta mechanism is changing this, yet the calculation still assumes that current-offset minus chainbase-offset equals chain-length. This appears to be wrong. This patch corrects the calculation by means of using the chainlength function if Generaldelta is used.