In the release notes "git status" was not mentioned, also shortly explain
the "-dirty" output generated by diff.
Added a paragraph to the "Pitfalls with submodules" section in
user-manual.txt describing new and old behavior of "git status" and "git
diff" for dirty submodules.
Signed-off-by: Jens Lehmann <Jens.Lehmann@web.de> Signed-off-by: Junio C Hamano <gitster@pobox.com>