changelog: add a line about improved prune documentation

changelog: reorder content

prune: more human-friendly documentation The previous help string generally had a highly technical language. I've tried my best to address that.

prune: improve help first line The previous help string for prune didn't mention successors in the first line. Note: Pierre-Yves David changed the original "hidden" to "obsolete" as it is better concept to put forward. (a bit more specific and with more consequence than just "hidden"). We need a good `hg help obsolete/obsolescence` result. We'll try to get this in the next version.

prune: try to clarify the "multi" revisions case I hope this highlight the use case for all three options.

prune: move help about biject after the one about split and fold The --biject flag seems a less common use case.

prune: no longer consider dropping --biject Field testing show it save people one wrong call often enough that it is worth keeping.

prune: more human-friendly documentation for --biject

prune: use ``-s/--succ`` in documentation Extracted by Pierre-Yves David

branching: merge with stable

compat: import the module dagutil module in evolve Discovery code is core have been rewritten to no longer depends on dagutil and the module have been removed. This break evolve's obsmarker discovery (older version of the discovery use the same concept).. A quick work around is to import the dagutil module in evolve and use that for now.

evolve: delete evolvestate after aborting interrupted `next --evolve` We didn't use to delete the evolvestate after aborting an interrupted `next --evolve`. This patch makes sure we do that. The test changes demonstrate the fix and we add a CHANGELOG entry about the fix.