style: silence another flak8 warning Default should be green now.

oops: backed out changeset df22f010cf24 pushed by error The changeset still fails some test

next: make next command --evolve by default Before this patch, if we need to evolve to update to the next child, we were suggesting the user to use --evolve flag. This patch make some changes to evolve by default in that conditions. After making next command to evolve by default we have to consider the following points: 1) If we don't need to evolve while updating to the next child: a) And if wdir is dirty, we suggest to use --merge flag b) if wdir is clean, we simply update to next child (if ambiguous, prompt the user to select one) 2) If we need to evolve: a) when wdir is dirty, we suggest the user to use `hg shelve` first, to make wdir clean. As we don't support --merge while evovling. b) when wdir is clean, we evolve the next cset. Changes made in test-prev-next.t reflect the changed behaviour.

next: improve the message for dirty working copy with --evolve This will be important soon when --evolve will be the default.

next: use the `hint` argument of bail if changed The argument is availabel since Mercurial 4.1. So let's use it.

prev: use the `hint` argument of bail if changed The argument is availabel since Mercurial 4.1. So let's use it.

next: explicitly specify --no-evolve in the tests The default value for this flag is about to switch.

branching: merge with stable

style: fix various flake8 warning

next: set if we need to evolve or not; also move logic to appropriate pos set the value `needevolve` and also move the logic to find aspiringchildren to appropriate position i.e before we suggest user to use other flags like --merge.