Updates for dirty submodules in release notes and user manual

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>

Documentation/RelNotes-1.7.0.txt

@@ -200,11 +200,13 @@ release, unless otherwise noted.
    from non-root dir, 2010-01-26) may be merged to older maintenance
    branches.
 
- * When "git diff" is asked to compare the work tree with something,
-   it used to consider that a checked-out submodule with uncommitted
-   changes is not modified; this could cause people to forget committing
-   these changes in the submodule before committing in the superproject.
-   It now considers such a change as a modification.
+ * When using "git status" or asking "git diff" to compare the work tree
+   with something, they used to consider that a checked-out submodule with
+   uncommitted changes is not modified; this could cause people to forget
+   committing these changes in the submodule before committing in the
+   superproject. They now consider such a change as a modification and
+   "git diff" will append a "-dirty" to the work tree side when generating
+   patch output or when used with the --submodule option.
 
 --
 exec >/var/tmp/1

Documentation/user-manual.txt

@@ -3640,6 +3640,26 @@ Did you forget to 'git add'?
 Unable to checkout '261dfac35cb99d380eb966e102c1197139f7fa24' in submodule path 'a'
 -------------------------------------------------
 
+In older git versions it could be easily forgotten to commit new or modified
+files in a submodule, which silently leads to similar problems as not pushing
+the submodule changes. Starting with git 1.7.0 both "git status" and "git diff"
+in the superproject show submodules as modified when they contain new or
+modified files to protect against accidentally committing such a state. "git
+diff" will also add a "-dirty" to the work tree side when generating patch
+output or used with the --submodule option:
+
+-------------------------------------------------
+$ git diff
+diff --git a/sub b/sub
+--- a/sub
++++ b/sub
+@@ -1 +1 @@
+-Subproject commit 3f356705649b5d566d97ff843cf193359229a453
++Subproject commit 3f356705649b5d566d97ff843cf193359229a453-dirty
+$ git diff --submodule
+Submodule sub 3f35670..3f35670-dirty:
+-------------------------------------------------
+
 You also should not rewind branches in a submodule beyond commits that were
 ever recorded in any superproject.