Resync the DCO text with upstream at http://developercertificate.org/

```
Everyone is permitted to copy and distribute verbatim copies of this
license document, but changing it is not allowed.
```

Docker-DCO-1.1-Signed-off-by: Andrew Page <admwiggin@gmail.com> (github: tianon)
Add authenticated TLS support for API

Docker-DCO-1.1-Signed-off-by: Johannes 'fish' Ziemke <github@freigeist.org> (github: discordianfish)
Add proper support for relative WORKDIR instructions

Docker-DCO-1.1-Signed-off-by: Andrew Page <admwiggin@gmail.com> (github: tianon)
Improve WORKDIR test to cover more edge cases

Docker-DCO-1.1-Signed-off-by: Andrew Page <admwiggin@gmail.com> (github: tianon)
Add some documentation about relative WORKDIR values

Docker-DCO-1.1-Signed-off-by: Andrew Page <admwiggin@gmail.com> (github: tianon)
refactor($hack,$docs): be consistent in apt-key keyserver URI usage, as done in #4740

In #4740, the apt-key call in docs is changed to use the keyserver port 80 instead of
port 11371, as the previous call would fail with a restrictive firewall or proxy.
This commit extends the change to all apt-key calls in the repository.

Docker-DCO-1.1-Signed-off-by: Viktor Vojnovski <vojnovski@gmail.com> (github: vojnovski)
Merge pull request #4754 from vojnovski/consistent_apt-key_use

refactor($hack,$docs): be consistent in apt-key keyserver URI usage
configurable dns search domains

Add a --dns-search parameter and a DnsSearch
configuration field for specifying dns search
domains.

Docker-DCO-1.1-Signed-off-by: Daniel Norberg <daniel.norberg@gmail.com> (github: danielnorberg)
Merge pull request #4691 from tianon/relative-workdir

Add proper support for relative WORKDIR instructions
Docker-DCO-1.1-Signed-off-by: Aditya <aditya@netroy.in> (github: netroy)

document `DisableNetwork` config flag
images: assurance and debug info on image layers

when pushing or saving layers, report sizes for validation. And ensure
that the files written are sync'ed.

Docker-DCO-1.1-Signed-off-by: Vincent Batts <vbatts@redhat.com> (github: vbatts)
Merge pull request #4777 from vbatts/vbatts-server-info_and_assurance

images: assurance and debug info on image layers
Remove duplication of Dns in config merging.

Fixes #4714
Docker-DCO-1.1-Signed-off-by: Alexandr Morozov <lk4d4math@gmail.com> (github: LK4D4)
fix typo in documentation

Docker-DCO-1.1-Signed-off-by: Daniel Norberg <daniel.norberg@gmail.com> (github: danielnorberg)
variable declaration cleanup

Docker-DCO-1.1-Signed-off-by: Daniel Norberg <daniel.norberg@gmail.com> (github: danielnorberg)
fix failing test to use kill instead of stop

TestCreateStartRestartStopStartKillRm was failing because stop has been
changed to not kill containers.

Docker-DCO-1.1-Signed-off-by: Cristian Staretu <cristian.staretu@gmail.com> (github: unclejack)
Merge pull request #3774 from danielnorberg/dns-search-domains

configurable dns search domains
Merge pull request #4703 from netroy/patch-1

Document the missing `DisableNetwork` config flag to /containers/create end-point
Merge branch 'https_client' of github.com:discordianfish/docker into discordianfish-https_client

Docker-DCO-1.1-Signed-off-by: Victor Vieux <victor.vieux@docker.com> (github: vieux)
Merge branch 'master' into discordianfish-https_client

Docker-DCO-1.1-Signed-off-by: Victor Vieux <victor.vieux@docker.com> (github: vieux)