git-commit: show --summary after successful commit.

Sometimes people accidentally commit files in wrong mode bits.
Show --summary output for the HEAD commit after successful commit
as a final sanity check.

Signed-off-by: Junio C Hamano <junkio@cox.net>

Documentation/tutorial-2.txt

@@ -23,6 +23,7 @@ $ echo 'hello world' > file.txt
 $ git add .
 $ git commit -a -m "initial commit"
 Committing initial tree 92b8b694ffb1675e5975148e1121810081dbdffe
+ create mode 100644 file.txt
 $ echo 'hello world!' >file.txt
 $ git commit -a -m "add emphasis"
 ------------------------------------------------

git-commit.sh

@@ -629,4 +629,7 @@ if test -x "$GIT_DIR"/hooks/post-commit && test "$ret" = 0
 then
 	"$GIT_DIR"/hooks/post-commit
 fi
+
+test "$ret" = 0 && git-diff-tree --summary --root --no-commit-id HEAD
+
 exit "$ret"