Note to self: never try to move submodules again

To migrate your existing submodules (more or less):

	set -x
	set -e

	mkdir .git/modules/pkg
	for old in */*/src ; do
	        new="pkg/${old#*/}"
	        if ! [ -f "$old/.git" ] || [ "${old%%/*}" = pkg ] ; then
			continue
		fi
		git -C ".git/modules/$old" config core.worktree "../../../../../$new"
		rmdir "$new"
		mv "$old" "$new"
	        sed -e "s,$old,$new," "$new/.git" > "$new/.git.tmp"
	        mv "$new/.git.tmp" "$new/.git"
		mkdir ".git/modules/${new%/src}"
	        mv ".git/modules/$old" ".git/modules/$new"

		rm "${old%/src}"/*.ninja
		mv "${old%/src}"/*.tar.{gz,xz,bz2} "${new%/src}/"
		rmdir "${old%/src}" || true
	done
	sed -e 's,^\[submodule "[^/]*/,[submodule "pkg/,' .git/config > .git/config.tmp
	mv .git/config.tmp .git/config

Even though it is not generally useful, it is easy to forget to update if it is
hidden.