drophack: major speedup to marker stripping It appear that each call to obsstore.add have a significant overhead (in particular the creation of a set form the list of markers and file system operation to the obsstore file. We now compute the marker we need to store and write them in a single call.

evolve: add a cmddebugrecordpruneparents command This command can be used to create prune marker with parent information from prune marker on changeset known locally.