evolve: add relevant marker exchange machinery This is going to be needed for obsolescence marker exchange.

fastobs: rename var from `node` to `rev` It contains revision (from repo.revs not node).

fastobs: move the extension to the hgext dir

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.

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

debugobsstorestat: add test for pruning There is multiple prune specific code in this command. So we test it in the presence of prun marker too.

debugobsstorestat: add information about cluster We now display information about independant osolescence markers clusters.

evolve: fix creation of prunedchildren for merge The `p2` code path was broken. (stupid typo)

evolve: add a debugobsstorestat command This commands print multiple some data about the content of the obsstore. This will be usefull to provide some metric and insight for obsolescence marker exchange.