fix(CONTRIBUTING): Developer Certificate of Origin w/o Grant

In 7fb55f77250a9b52b0515a7e655ecc605ae452ca the DCO lost the grant so
change the title back to just DCO.

Docker-DCO-1.1-Signed-off-by: Brandon Philips <brandon.philips@coreos.com> (github: philips)
Move UserLookup functionality into a separate pkg/user submodule that implements proper parsing of /etc/passwd and /etc/group, and use that to add support for "docker run -u user:group" and for getting supplementary groups (if ":group" is not specified)

Docker-DCO-1.1-Signed-off-by: Andrew Page <admwiggin@gmail.com> (github: tianon)
Use type switch instead of reflection

Docker-DCO-1.1-Signed-off-by: Michael Crosby <michael@crosbymichael.com> (github: crosbymichael)
Consolidate a bunch of the supplementary-groups tests to cut down on the number of RUN lines in a single Dockerfile within TestBuild

Docker-DCO-1.1-Signed-off-by: Andrew Page <admwiggin@gmail.com> (github: tianon)
Update lxc_template.go

If networking is disabled, but then pipework is used later to add nics, the network still doesn't function. Using flags=up for empty networking fixes this.
Docker-DCO-1.1-Signed-off-by: James DeFelice <james.defelice@ishisystems.com> (github: jdef)
Fix RST formatting
New folder structure to support TextMate2 bundles format

Docker-DCO-1.1-Signed-off-by: German Del Zotto <germ@ndz.com.ar> (github: GermanDZ)
Instructions for Textmate's bundle installation

Docker-DCO-1.1-Signed-off-by: German Del Zotto <germ@ndz.com.ar> (github: GermanDZ)
please, for the love of Docker, do. not. use. symlinks

Docker-DCO-1.1-Signed-off-by: Sven Dowideit <SvenDowideit@fosiki.com> (github: SvenDowideit)
Merge pull request #3987 from SvenDowideit/warn-against-symlinks

please, for the love of Docker, do. not. use. symlinks
Remove panic in lxc driver.

Docker-DCO-1.1-Signed-off-by: Guillaume J. Charmes <guillaume.charmes@docker.com> (github: creack)
Add set master for interface
Docker-DCO-1.1-Signed-off-by: Michael Crosby <michael@crosbymichael.com> (github: crosbymichael)
Add network set interface in namespace by pid
Docker-DCO-1.1-Signed-off-by: Michael Crosby <michael@crosbymichael.com> (github: crosbymichael)
Swap Firefox to Iceweasel so that the Desktop Integration example is simplified and easier to understand

Docker-DCO-1.1-Signed-off-by: Andrew Page <admwiggin@gmail.com> (github: tianon)
Use c to change interface name
Docker-DCO-1.1-Signed-off-by: Michael Crosby <michael@crosbymichael.com> (github: crosbymichael)
devmapper: Enable skip_block_zeroing

This makes the device mapper not zero out blocks allocated on the
thinp device. This is safe in our use case, as we access the device
via a filesystem that doesn't leak any uninitialized data to userspace.

This partially helps with https://github.com/dotcloud/docker/issues/3280
and should generally improve preformance on the devicemapper backend.

Docker-DCO-1.1-Signed-off-by: Alexander Larsson <alexl@redhat.com> (github: alexlarsson)
Add bidirectional iptables rule back to links

Fixes #4014
Docker-DCO-1.1-Signed-off-by: Michael Crosby <michael@crosbymichael.com> (github: crosbymichael)
Remove linux specific calls

Docker-DCO-1.1-Signed-off-by: Guillaume J. Charmes <guillaume.charmes@docker.com> (github: creack)
Replace my C code with tianons Go code
Docker-DCO-1.1-Signed-off-by: Michael Crosby <michael@crosbymichael.com> (github: crosbymichael)
Adjust test to match its comment

Docker-DCO-1.1-Signed-off-by: Andrew Williams <williams.andrew@gmail.com> (github: TheDude05)