Merge branch 'sb/submodule-rm-absorb'

"git rm" used to refuse to remove a submodule when it has its own git repository embedded in its working tree. It learned to move the repository away to $GIT_DIR/modules/ of the superproject instead, and allow the submodule to be deleted (as long as there will be no loss of local modifications, that is). * sb/submodule-rm-absorb: rm: absorb a submodules git dir before deletion submodule: rename and add flags to ok_to_remove_submodule submodule: modernize ok_to_remove_submodule to use argv_array submodule.h: add extern keyword to functions