Extending DistKV

DistKV comes with a built-in extension mechanism for its command line, based on Python namespaces and import hackery.

Yor extension needs to ship a distkv_ext.NAME module with a command.py or a client.py module (or both, if required). This adds the command NAME to distkv or distkv client, respectively.

This method is not zip-safe because it injects a main global into the code. Fixing this is TODO.