Remove bsdtar by checking magic
Add unit tests for tar/untar with multiple compression + detection
Update docs
Merge branch 'master' into remove_bsdtar

Conflicts:
	docs/sources/contributing/devenvironment.rst
Fix bug on compression detection when chunck < 10bytes
Remove bsdtar dependency in various install scripts
Fix issue within TestDelete. The archive is now consumed by graph functions
Merge branch 'remove_bsdtar' of https://github.com/dotcloud/docker into remove_bsdtar
Merge pull request #885 from dotcloud/remove_bsdtar

* Runtime: Remove bsdtar dependency