Upload multiple files in a single rsync command.

As with gets, this makes uploads 3x faster at least.

multi_put() is now renamed simply put(), and the old single-path put() is no more.

All tests pass (including the rsync ones), plus I've tried this out on 1000 files in our real repo.
There are a few instances where you do this instead of os.path.join. Is there a reason?