Make the rest of commands work from a subdirectory.

These commands are converted to run from a subdirectory.

    commit-tree convert-objects merge-base merge-index mktag
    pack-objects pack-redundant prune-packed read-tree tar-tree
    unpack-file unpack-objects update-server-info write-tree

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

unpack-file.c

@@ -29,6 +29,8 @@ int main(int argc, char **argv)
 	if (argc != 2 || get_sha1(argv[1], sha1))
 		usage("git-unpack-file <sha1>");
 
+	setup_git_directory();
+
 	puts(create_temp_file(sha1));
 	return 0;
 }