When a submodule commit had already been staged and another commit had
been checked out inside the submodule, the diff always displayed the
submodule commit log messages between the last supermodule commit and
the working tree, totally ignoring the commit in the index.
Signed-off-by: Jens Lehmann <Jens.Lehmann@web.de> Signed-off-by: Shawn O. Pearce <spearce@spearce.org>