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)
Fix a few miscellaneous typos (Unkown -> Unknown, Recieve -> Receive)

Docker-DCO-1.0-Signed-off-by: Andrew Page <admwiggin@gmail.com> (github: tianon)
google-compute-engine: fix typos
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)
Hello World: fix detach behavior

The hello world example relies on being able to exit the container attachment using Control-C without stopping it. According to this thread (and my own experience), this doesn't work anymore:

https://groups.google.com/forum/#!msg/docker-user/nWXAnyLP9-M/kbv-FZpF4rUJ

Added -sig-proxy=false to the attach command.
Add the customary bold
Merge pull request #3499 from tianon/typos

Fix a few miscellaneous typos (Unkown -> Unknown, Recieve -> Receive)
Merge pull request #3501 from proppy/patch-1

google-compute-engine: fix typos
Merge pull request #3503 from gertvv/patch-1

Hello World: fix detach behavior
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