This update for docker-distribution fixes the following issues:

- Updated version 2.1.1 to 2.4.0
+ New S3 storage driver
* The default s3 storage driver is now implemented on top of the official Amazon
S3 SDK, boasting major performance and stability goodness. The previous storage
is still available, but deprecated.
+ Garbage Collector
* A garbage collector tool has been added to the registry. For more details see
the garbage collector documentation.
+ Tagged Manifest Events
* Manifest push and pull events will now include the tag which was used in the
operation (if applicable).
+ Relative URLs
* The registry can now be configured to return relative URLs in Location headers.
+ V1 Signature disabled
* With the ongoing adoption of the schema 2 manifest format and deprecation of
signatures, this option will improve pull performance by generating and
returning a single libtrust signature.
+ Gotchas
* The RADOS storage driver has been removed. The registry can still be used with
Ceph as the storage backend using the swift driver in conjunction with the
Swift API gateway.
* The command line format has changed to support subcommands. To run a registry
as before an additional subcommand - serve - is required.
* The legacy S3 storage driver, based on adroll/goamz is now deprecated and will
be removed in a future release.

+ Allow uppercase characters in hostnames.
+ Fix schema1 manifest etag and docker content digest header.
+ Add option to disable signatures.
+ To avoid any network use unless necessary, delay establishing authorization.
+ Extend authChallenger interface to remove type cast.
+ Enable proxying registries to downgrade fetched manifests to Schema 1.
+ Support the Image Manifest Version 2, Schema 2 manifest format.