tarsum: include xattr headers in to the checksum

this is to enhance the tarsum algorithm, but _MUST_ be done in lock step
with the same for docker-registry. (PR will be cited)

Docker-DCO-1.1-Signed-off-by: Vincent Batts <vbatts@redhat.com> (github: vbatts)
tarsum: version the addition of xattrs

Now that TarSum can be versioned, move the addition of xattr headers in
to the next version of TarSum

Signed-off-by: Vincent Batts <vbatts@redhat.com>
Consistently use 'sudo docker' in examples

Docker-DCO-1.1-Signed-off-by: Sven Dowideit <SvenDowideit@docker.com> (github: SvenDowideit)
Added missing 't' from the end of the /images/{{id}}/get eg.

Docker-DCO-1.1-Signed-off-by: Sven Dowideit <SvenDowideit@docker.com> (github: SvenDowideit)
Merge pull request #8060 from SvenDowideit/missing-t-in-get-api-eg

Added missing 't' from the end of the /images/{{id}}/get eg.
Merge pull request #8056 from SvenDowideit/use-sudo-docker-everywhere

Consistently use 'sudo docker' in examples
Merge pull request #5977 from vbatts/vbatts-tarsum_xattrs

tarsum: include xattr headers in to the checksum