Merge branch 'gc/branch-recurse-submodules-fix'

A handful of obvious clean-ups around a topic that is already in 'master'. * gc/branch-recurse-submodules-fix: branch.c: simplify advice-and-die sequence branch: rework comments for future developers branch: remove negative exit code branch --set-upstream-to: be consistent when advising branch: give submodule updating advice before exit branch: support more tracking modes when recursing