revlog: improve delta generation heuristics for generaldelta Without this change, pulls (and clones) into a generaldelta repository could generate very inefficient revlogs, the size of which could be at least twice the original size. This was caused by the generated delta chains covering too large distances, causing new chains to be built far too often. This change addresses the problem by forcing a delta against second parent or against the previous revision, when the first parent delta is in danger of creating a long chain.