Allow for use of the tarfile Python module in the archive state.

Hi :-)

I was attempting to use the archive state on Solaris 10, however tar on Solaris 10 doesn't support the compression arguments (eg z or j).

Hence, I was thinking it might be a solution to use the Python tarfile module where possible, whilst still allowing the use of the tar executable if needed. Making for a more platform-independent solution.

I'm more than happy to change any of this if anything's wrong :-)

I've tried it out on Solaris 10 and Ubuntu Saucy, and it all seems fine (famous last words :-p ) the old code is all still there, so nothing should regress (I don't think).

Cheers :-)