cat-file: make it work in a subdirectory.

Signed-off-by: NJunio C Hamano <junkio@cox.net>
(cherry picked from 73244994ee4abd6e436e8a1d597dd917271d77a9 commit)

cat-file.c

@@ -12,6 +12,7 @@ int main(int argc, char **argv)
 	void *buf;
 	unsigned long size;
 
+	setup_git_directory();
 	if (argc != 3 || get_sha1(argv[2], sha1))
 		usage("git-cat-file [-t | -s | <type>] <sha1>");