Attempt to fix issue #5.

Override the insync method to ignore 'unknown' as not being in sync if
ignore_impossible_operations is set to true.

This has a unit test, but I'm not sure it'll actually work (due to the way
puppet mangles values, we may get 'true' or :true instead of true..

Also ignore_impossible_operations is horribly named, suggestions welcome.

We should also have a version which throws an exception (i.e. fails, rather
than just doesn't converge).
Fix typo, fixes issue #7
Add 10G too, as we do have machines with this speed
Set speed and duplex together.

We already do this when setting the duplex, so lets do it when setting speed.
I think this will fix issue #8