CONTRIBUTING.md: wrap DCO to 78 chars per line

The DCO is a bit hard to read on Github right now because there is lots
of horizontal scrolling. Reformat it to 78 chars per line like the rest
of the file.

Example: http://imgur.com/LtJEIsl

Docker-DCO-1.1-Signed-off-by: Brandon Philips <brandon.philips@coreos.com> (github: philips)
Stop ADD from following symlinks outside the context when passed as the first argument

Docker-DCO-1.1-Signed-off-by: Andrew Page <admwiggin@gmail.com> (github: tianon)
Use https to get the latest docker version

To avoid unexpected results since docker was using http.
For instance, my broadband doesn't return not found when it's down but
a html page saying that the internet is down. Docker was showing that
html instead of ignoring it.

Fix #3570

Docker-DCO-1.1-Signed-off-by: Fabio Falci <fabiofalci@gmail.com> (github: fabiofalci)
Add xz-utils to our deb-recommends since it's necessary for some images

Docker-DCO-1.1-Signed-off-by: Andrew Page <admwiggin@gmail.com> (github: tianon)
Remove reference to nonexistent CONFIG_UID_NS

Docker-DCO-1.1-Signed-off-by: Andrew Page <admwiggin@gmail.com> (github: tianon)
Fix docs typo: "Gento" -> "Gentoo"

Docker-DCO-1.1-Signed-off-by: Andrew Page <admwiggin@gmail.com> (github: tianon)
Added document explaining openSUSE installation

Added a new documentation page explaining how to install Docker on
openSUSE.

Docker-DCO-1.1-Signed-off-by: Flavio Castelli <fcastelli@suse.com> (github: flavio)
Merge pull request #3587 from tianon/fix-gentoo-typo

Fix docs typo: "Gento" -> "Gentoo"
Merge pull request #3570 from fabiofalci/3569-validate-docker-version

Fetch docker version over https
Un-gofmt ./vendor

We can't be modifying this except to update from upstream.

Docker-DCO-1.1-Signed-off-by: Andrew Page <admwiggin@gmail.com> (github: tianon)
Merge pull request #3534 from philips/reformat-DCO

CONTRIBUTING.md: wrap DCO to 78 chars per line
Merge pull request #3591 from tianon/fix-vendor

Un-gofmt ./vendor
Fix Travis to not check gofmt on vendor/*

Docker-DCO-1.1-Signed-off-by: Andrew Page <admwiggin@gmail.com> (github: tianon)
Fix "foo: no such file or directory" test failure, and normalize creation of custom error to always depend on if os.IsNotExist(err) so we don't hide other errors that might crop up in these tests

Docker-DCO-1.1-Signed-off-by: Andrew Page <admwiggin@gmail.com> (github: tianon)
Merge pull request #3586 from flavio/add_openSUSE_installation_docs

Added document explaining openSUSE installation
Merge pull request #3585 from tianon/remove-uid-ns-reference

Remove reference to nonexistent CONFIG_UID_NS
Merge pull request #3567 from tianon/dockerfile-add-symlink

Stop ADD from following symlinks outside the context when passed as the first argument
Merge pull request #3592 from tianon/fix-travis-vendor

Fix Travis to not check gofmt on vendor/*
Merge pull request #3581 from tianon/deb-xz-utils

Add xz-utils to our deb-recommends since it's necessary for some images