evolve: return the new replacement node to be stored in evolvestate While resolving phase-divergence, we can end up obsoleting the phase-divergent commit in favor of the public commit. Before this patch we return the node of public commit to store as a replacement of the phase-divergent commit. The above will not cause any problem till the time we use `hg evolve --abort` on an interrupted evolve which tries to strip the replacement nodes because it thinks that the replacements nodes are the ones which are created during the resolution and are new. Since we will be stripping a public node, `evolve --abort` will error out saying cannot strip public changeset, unable to abort evolve which is bad. We should make sure, replacements should only consist of new nodes formed. If the instablity is resolved by obsoleting in favour of old changeset, we should not store the old changeset in replacements in evolvestate.

#require test-repo pyflakes

Copied from Mercurial core (60ee2593a270)

  $ cd "`dirname "$TESTDIR"`"

run pyflakes on all tracked files ending in .py or without a file ending
(skipping binary file random-seed)

  $ hg locate 'set:(**.py or grep("^#!.*python")) - removed()' 2>/dev/null \
  > | xargs pyflakes 2>/dev/null