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