Add Developer Certificate of Origin Text

We purposely chose to license Docker under the Apache 2.0 license. This is a well-known
license, which is popular for its permissive and flexible properties, while still
encouraging a collaborative community. It also makes certain representations with regard
to contributions, and the rights given to contributors, the project, people who use Docker,
people who modify Docker, etc.

This approach to contributions is inspired by the popular Linux Developer
"Certificate of Origin". This approach makes it simple for new contributors to get started,
and avoids bureaucracy in tracking contributions and contributors.

To indicate accordance, each individual contribution to the Project is signed off by the
developer, using his or her real name, email address, and github handle in the format below:

	Docker-DCO-1.0-Signed-off-by: Joe Smith <joe.smith@email.com>
Merged with master
hack/PACKAGERS.md: libdevmapper
Fix typos in Vagrantfile
Updated Introduction link

Previously the introduction link pointed to www.docker.io. That
did not seem to make a lot of sense to me so instead I pointed it
at:

http://www.docker.io/learn_more/
Reimplement lxc-ps

Instead of calling lxc-ps in top endpoint, we reimplement it by
calling ps and filter for pids running in a given container.
Fix and re-enable TestGetContainersTop
Update binaries.rst

Along with the kernel requirement, you need a working copy of lxc.  When trying to start using "/docker -d", received error 'initapi: exec: "lxc-start": executable file not found in $PATH'
Allow to use -H unix:// like -H tcp://
Improve TestParseHost
Factor cache-probing logic out of buildfile.commit() and CmdRun().
Record added-tree sha256 in buildfile.CmdAdd, probe and use cache.
Add testcases for ADD caching, closes #880.
Add self to AUTHORS.
Add CHANGELOG.md entry for ADD caching.
Added warning when browsing master. & no longer hides alternative versions.
Always copy dockerinit locally, regardless of whether our docker binary is static, because even it might get deleted or moved/renamed
Add dockerinit SHA1 and path to "docker info" when debug mode is enabled
Allow packagers to specify a custom dockerinit lookup location via DOCKER_INITPATH in dynbinary

Only necessary if distro policy dictates that the path deviate from the paths already listed in utils/utils.go - please refrain from using it otherwise.
Fix "go tool cover" detection to only add -cover and -coverprofile if we both have cover support in Go, and if we have the cover tool downloaded