Merge branch 'bw/push-submodule-only'

"git submodule push" learned "--recurse-submodules=only option to push submodules out without pushing the top-level superproject. * bw/push-submodule-only: push: add option to push only submodules submodules: add RECURSE_SUBMODULES_ONLY value transport: reformat flag #defines to be more readable