After cloning a repository with 'git clone --recurse-submodules' I
should be able to add a file with 'git add --recurse-submodules' to
avoid worrying about submodule boundaries.

This is not like normal 'git add' since to avoid lots of meaningless
commits it would not create a commit in the submodule and the change
therefore could not be immediately reflected in the superproject
index.  Maybe something like the following would work:

	$ git clone --recurse-submodules https://gerrit.googlesource.com/gerrit
[...]
	$ echo hi >plugins/cookbook-plugin/greeting
	$ git add --recurse-submodules .
	M plugins/cookbook-plugin
	$ git commit --recurse-submodules
	# Please enter a commit message for your changes to
	# plugins/cookbook-plugin.
	# Lines starting with '#' will be ignored, and an empty message
	# aborts the commit.

	_