rebase: only show stat if configured to true

If rebase.stat is set to true, a diffstat should be displayed. If it is
not set, it should default to false. However, if it is explicitly set to
false (or other value), a diffstat is still displayed, which is probably
not what most users would expect. Show diffstat only if it is set
to true.

Signed-off-by: Martin von Zweigbergk <martin.von.zweigbergk@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

git-rebase.sh

@@ -48,7 +48,8 @@ do_merge=
 dotest="$GIT_DIR"/rebase-merge
 prec=4
 verbose=
-diffstat=$(git config --bool rebase.stat)
+diffstat=
+test "$(git config --bool rebase.stat)" = true && diffstat=t
 git_am_opt=
 rebase_root=
 force_rebase=