stash: end index commit log with a newline

There was no newline at the end of the index commit message, putting
the shell prompt at its end after a 'git cat-file commit $id'.  This is
similar to what was fixed in 843103d693.

Signed-off-by: Jean-Luc Herren <jlh@gmx.ch>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

git-stash.sh

@@ -57,7 +57,7 @@ save_stash () {
 
 	# state of the index
 	i_tree=$(git write-tree) &&
-	i_commit=$(printf 'index on %s' "$msg" |
+	i_commit=$(printf 'index on %s\n' "$msg" |
 		git commit-tree $i_tree -p $b_commit) ||
 		die "Cannot save the current index state"