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.

evolve: extend obsstore object to use prune parent information Now that we have the information, we can use it to build a mapping to access all marker that prune a children of a node. This is similar to what we do for successors and precursors. The performance impact is a few tens of second on my mercurial clone. Experimenting is worth the trouble.

prune: wrap mercurial internal to add parent information in prune marker We store as a p1 (and p2) key in the extra dict for marker. This allow us to record this information for future use without requiering a format change.

evolve: drop `latercomer` and `conflicting` compatibility. Those old alias are deprecated for a long time now. All computations related to troubles are in Mercurial core for multiple versions.