Fix order of options to tar

The order of options being passed to tar isn't quite correct. The file to be extracted is a actually a parameter to the "f" option in the command line being passed. I've changed the order and added a space to the existing parameters so that extra options passed as extract_flags do not get appended to the end of the filename.

There are a few cases where this will still cause problems, but it's better than the current code, as passing *any* extract_flags will currently break tar.