Kill fastobs, as marmoute says it causes problems

tests: fix test-prune.t breakage test-prune.t was broken due to 91d28bd0e04e in upstream Mercurial, which made hidden commits visible when a local tag made the commit reachable. The fix is to delete the tag in the test.

Fix preservation of rename information on evolve (#33) Following what rebase itself does, call duplicatecopies between rebasenode and concludenode. Should fix https://bitbucket.org/marmoute/mutable-history/issue/33/evolve-command-loses-copy-metadata