+ Builder: ADD of a local file will detect tar archives and unpack them
	into the container instead of copying them as a regular file.

* Builder: ADD uses tar/untar for copies instead of calling 'cp -ar'.
	This is more consistent, reduces the number of dependencies, and
	fixe #896.
Merge pull request #897 from dotcloud/fix-overlapping-add

* Builder: ADD improvements: use tar for copy + automatically unpack local archives