push: make locking of source optional (issue3684) Having the permission to lock the source repo on push is now optional. When the repo cannot be locked, phase are not changed locally. A status message is issue when some actual phase movement are skipped: cannot lock source repo, skipping local public phase update A debug message with the exact reason of the locking failure is issued in all case.

push: factorise phase movement in a simple closure Having all phases movement centralised will help to handle special case when the local repo can not be locked as describe in issue 3684.