bundle2: automatically add 'targetphase' parameter in writenewbundle
If we are bundling secret changeset and the bundle will contain phase, we
request the changegroup to be applied as secret.
It will be useful for next patch as we are now sure that secrets changesets
are applied as secret and not applied as draft then forced to secret.
Our full contribution guidelines are in our wiki, please see:
https://www.mercurial-scm.org/wiki/ContributingChanges
If you just want a checklist to follow, you can go straight to
https://www.mercurial-scm.org/wiki/ContributingChanges#Submission_checklist
If you can't run the entire testsuite for some reason (it can be
difficult on Windows), please at least run `contrib/check-code.py` on
any files you've modified and run `python contrib/check-commit` on any
commits you've made (for example, `python contrib/check-commit
273ce12ad8f1` will report some style violations on a very old commit).