In case of bad download, error given by is feeder is better than output
of compressor which claims data are missing

We now use system tar and gzip to compress/decompress payloads

Goals are:
- Speed-up extraction and creation of payloads.
- Allow to use non-python supported compressor like (pbzip2 and xz)
- Remove python2.7.1 tarfile.py module
- Remove python 2.7.1 gzip.py to avoid filename to be in gzip headers
- Remove gzipstream.py module used to stream gzip file

also optimize tarball.getnames

build -p recreate payload file if already exsits

is build now create payloads without version in name and create symplink with version to it.

This is very useful to avoid too many recreation of payload after adding to db or when bumping version

this also fix bad display of all changelog in verbose mode

we now have a changelog command, no needs to overload list output

we can now set a minimal installsystems version in your description
install will not be able to read those images

Add tarfile from python 2.7.2

This allow method add in Tarfile to have filter parameter.
This give us filter capa on file to include.
Should be removed when python 2.7 will be the minimum version

Because we roolback to python 2.6 requirment, we need to ship.

Signed-off-by: Sebastien Luttringer <sebastien.luttringer@smartjog.com>

is new have now an force option to overwrite existing images