phases: write default phase data as soon as possible.
Marks phase data as dirty when computing default phase. Actual writing is done
when the lock is released. So, read only operation don't write phase data
because they don't lock the repo.
push: return 1 if no changes found (
issue3228)
Currently we have the following return codes if nothing is found:
commit incoming outgoing pull push
intended 1 1 1 1 1
documented 1 1 1 0 1
actual 1 1 1 0 0
This fixes the lower-right entry.
push: more precise failure check on subrepo push
This will let us distinguish between nothing to push and push failed