docker daemon: initialize the daemon pidfile early

fixes https://github.com/dotcloud/docker/issues/6973

Docker-DCO-1.1-Signed-off-by: Vincent Batts <vbatts@redhat.com> (github: vbatts)
Fix cap drop issues with lxc

This uses "," instead of spaces so that the flags are parsed correctly
and also does not do a strings.Split on an empty string because
strings.Split will return a slice with one element, and empty string
causing parsing to fail when it validates that the cap exists.
Docker-DCO-1.1-Signed-off-by: Michael Crosby <michael@docker.com> (github: crosbymichael)
Use : to split caps in sysinit flags
Docker-DCO-1.1-Signed-off-by: Michael Crosby <michael@docker.com> (github: crosbymichael)
archive/tar: update to fix writing of PAX headers

Docker-DCO-1.1-Signed-off-by: Cristian Staretu <cristian.staretu@gmail.com> (github: unclejack)
Skip whole dir dockerignoring with warning

Fixes #7093
Docker-DCO-1.1-Signed-off-by: Alexandr Morozov <lk4d4math@gmail.com> (github: LK4D4)
Updated Red Hat Enterprise Linux installation instructions for version 7

Docker-DCO-1.1-Signed-off-by: Brian Exelbierd <bex@pobox.com> (github: bcexelbi)
Update docs on --sig-proxy to indicate that SIGKILL and SIGSTOP cannot be proxied

Docker-DCO-1.1-Signed-off-by: Matt Heon <mheon@redhat.com> (github: mheon)
Improve data volume container example.
Docker-DCO-1.1-Signed-off-by: Jason Livesay <ithkuil@gmail.com> (github: runvnc)
initial work to make a mockup

Docker-DCO-1.1-Signed-off-by: SvenDowideit <SvenDowideit@home.org.au> (github: SvenDowideit)
The UX spec

Docker-DCO-1.1-Signed-off-by: SvenDowideit <SvenDowideit@home.org.au> (github: SvenDowideit)
dynamically load a /versions.html_fragment file so that all old versions get the complete dropdown list of versions to select

Docker-DCO-1.1-Signed-off-by: SvenDowideit <SvenDowideit@home.org.au> (github: SvenDowideit)
Fix a typo in the tutorial
resumablerequestreader: allow initial response

Make it possible to inspect an initial response and pass it to
ResumableRequestReader. This makes it possible to inspect an initial
response and passing it to ResumableRequestReader to avoid making an
extra request.

Docker-DCO-1.1-Signed-off-by: Cristian Staretu <cristian.staretu@gmail.com> (github: unclejack)
get layer: remove HEAD req & pass down response

Docker-DCO-1.1-Signed-off-by: Cristian Staretu <cristian.staretu@gmail.com> (github: unclejack)
docs/installation/google: update gcloud options

Docker-DCO-1.1-Signed-off-by: Johan Euphrosine <proppy@google.com> (github: proppy)
integration-cli: add more tests for BuildAddTar

Docker-DCO-1.1-Signed-off-by: Johan Euphrosine <proppy@google.com> (github: proppy)
integration-cli/TestBuildAddTar: generate context from test

Docker-DCO-1.1-Signed-off-by: Johan Euphrosine <proppy@google.com> (github: proppy)
archive: add buffers to operations with tarballs

Docker-DCO-1.1-Signed-off-by: Cristian Staretu <cristian.staretu@gmail.com> (github: unclejack)
archive: add a benchmark for TarUntar

Docker-DCO-1.1-Signed-off-by: Cristian Staretu <cristian.staretu@gmail.com> (github: unclejack)
Merge pull request #7104 from mheon/sigproxy_docs

Update docs on --sig-proxy