bundle2: use new compression engine API for compression
Now that we have a new API to define compression engines, let's put it
to use!
The new code stores a reference to the compression engine instead of
a low-level compressor object. This will allow us to more easily
transition to different APIs on the compression engine interface
once we implement them.
As part of this, we change the registration in bundletypes to use 'UN'
instead of None. Previously, util.compressors had the no-op compressor
registered under both the 'UN' and None keys. Since we're switching to
a new API, I don't see the point in carrying this dual registration
forward.
# name space package to host third party extensions
from __future__ import absolute_import
import pkgutil
__path__ = pkgutil.extend_path(__path__, __name__)