Merge branch 'hv/submodule-recurse-push'

"git push --recurse-submodules" learns to optionally look into the histories of submodules bound to the superproject and push them out. By Heiko Voigt * hv/submodule-recurse-push: push: teach --recurse-submodules the on-demand option Refactor submodule push check to use string list instead of integer Teach revision walking machinery to walk multiple times sequencially