Move extraction tests into their own file.

There's going to be a lot of special cases to test.
Neatly deal with archives which are completely empty.

They don't even make a top level directory.
Fix make_dist_local

There have been a bunch of changes to Gitpan::Dist that were not
reflected in this program.
Don't try to chmod links.

chmod will try to work on whatever its linked to.  If the link is
dangling, chmod will error.  chmod will get the file pointed to
eventually if it's in the archive.  If it's not in the archive, it
shouldn't be messing with it.

For #87
Merge branch 'feature/bad_archives'

For #87