teach magit-stage-item to add submodules
magit-wash-diff-section: revert accidental face change

Not that I think we need to use different faces here but stopping to do
so was not intentional.
Merge branch 'master' into next
magit-run-gitk: with a prefix argument don't use --all

Close #1288.
Merge branch 'master' into next

Conflicts:
	magit.el