this allow to register breaked or offline repository wihtou breaking all is

This will help remi to be cool and save some day in his life

Overide real chown method from tarfile which make crazy check about
uid/gid before chowning. This leads to bug when a uid/gid doesn't
exitsts on the running system

This overide as a sexy side effect which allow badly create tarball
(whithout --numeric-owner) to be extracted correctly

This fix is a workaround taking a class gzipstream from redhat (GPL2)
which allow gzip class to be not seekable.
Since python 3.2, gzip module is now not seekable. Until we swith to version
we should use this hack

THis is very useful to be able to list it !

new syntax is available [repo/]image[:version]
first command updated is delete

This also change underlying way of initiliaze a repository.
A repository can now be defined and be innaccessible