test-prune: update test with a prune output compatible with newest hg Newest hg can record the parent information in the marker. This change the debugobsstorestate output a lot.

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.