prune: add test and more robusness

prune: detect bad input We accept multiple changeset folded into one successors. One changesets split in multiple successors. But we refuse multiple changesets split in multiple ones.

simplify locking in prune

prune: rename --new to --succ This is closer to want the documentation says.

prune: improve command function name

prune: fix doc

evolve: drop uneeded noderange function We can use revrange instead