Fixed error in group add example

There is no ${USERNAME} in bash, only ${USER}
fix error on docker wait
give more specific advice on setting up signing

Docker-DCO-1.0-Signed-off-by: Sven Dowideit <SvenDowideit@fosiki.com> (github: SvenDowideit)
Update release checklist with more information, more commands, and more correct flow (test, upload to test.docker.io, test, upload to get.docker.io, THEN tag&merge)

Docker-DCO-1.0-Signed-off-by: Andrew Page <admwiggin@gmail.com> (github: tianon)
Update Makefile to use "docker:GIT_BRANCH" as the generated image name for increased versatility

... and other minor Makefile improvements :)

Docker-DCO-1.0-Signed-off-by: Andrew Page <admwiggin@gmail.com> (github: tianon)
Revert "Make sure the cache lookup returns always the same result"

This reverts commit 1d4b7d8fa1af95ce83f263a49ed24e686fa7cb62.

Docker-DCO-1.0-Signed-off-by: Sjoerd Langkemper <sjoerd@byte.nl> (github: Sjord)
Fix issue #3375 - Return most recent image from the cache

ImageGetCached searches for an image from the cache. Instead of returning the
first image it finds, it should return the most recently created image. When a
build with --no-cache then adds a new image with the same parameters, it is
used instead of the old, existing image.

Docker-DCO-1.0-Signed-off-by: Sjoerd Langkemper <sjoerd@byte.nl> (github: Sjord)
Disable compression for build. More space usage but much faster upload

Docker-DCO-1.0-Signed-off-by: Guillaume J. Charmes <guillaume.charmes@docker.com> (github: creack)
Potential fix for ADD .

Docker-DCO-1.0-Signed-off-by: Guillaume J. Charmes <guillaume.charmes@docker.com> (github: creack)
Make sure file are cached correctly during build

Docker-DCO-1.0-Signed-off-by: Guillaume J. Charmes <guillaume.charmes@docker.com> (github: creack)
Cleanup utils.Download

Docker-DCO-1.0-Signed-off-by: Guillaume J. Charmes <guillaume.charmes@docker.com> (github: creack)
Make sure the remote ADD are cached properly

Docker-DCO-1.0-Signed-off-by: Guillaume J. Charmes <guillaume.charmes@docker.com> (github: creack)
Merge pull request #3494 from tianon/makefile-use-branch-tag

Update Makefile to use "docker:GIT_BRANCH" as the generated image name
update REMOTE_TODO.md

Docker-DCO-1.0-Signed-off-by: Victor Vieux <victor.vieux@docker.com> (github: vieux)
Merge pull request #3514 from vieux/update_REMOTE_TODO

update REMOTE_TODO.md
Merge pull request #3510 from creack/hotfix-add_caching

Hotfix add caching
Merge pull request #3493 from SvenDowideit/commit-signoff-location

give more specific advice on setting up signing
Merge pull request #3464 from vieux/fix_error_wait

fix error on docker wait
Merge pull request #3417 from Sjord/use-most-recent-cache-image

Fix issue #3375 - Return most recent image from the cache
Merge pull request #3446 from tianon/update-checklist

Update release checklist with more information, more commands, and more ...