Merge branch 'fc/push-simple-updates-cleanup'

Some more code and doc clarification around "git push". * fc/push-simple-updates-cleanup: push: don't get a full remote object push: only check same_remote when needed push: remove trivial function push: remove redundant check push: factor out the typical case push: get rid of all the setup_push_* functions push: trivial simplifications push: make setup_push_* return the dst push: only get the branch when needed push: factor out null branch check push: split switch cases push: return immediately in trivial switch case push: create new get_upstream_ref() helper