builtin-commit: fix summary output.

Because print_summary() forgot to call diff_setup_done() after futzing with
diff output options, it failed to activate recursive diff, which resulted in
an incorrect summary.

Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin-commit.c

@@ -662,6 +662,7 @@ static void print_summary(const char *prefix, const unsigned char *sha1)
 	rev.show_root_diff = 1;
 	rev.commit_format = get_commit_format("format:%h: %s");
 	rev.always_show_header = 0;
+	diff_setup_done(&rev.diffopt);
 
 	printf("Created %scommit ", initial_commit ? "initial " : "");