docker load clears DockerVersion

[mpasternacki]

This prevents images created with Docker 0.12+, saved, and loaded from being pushed to registry, because without DockerVersion field, registry seems to expect lowercase id field rather than new Id (I get HTTP code 400 while uploading metadata: {"error": "Missing keyid' in JSON"}`).

Reproduction:

vagrant@packer-debian-7:~/i$ cat Dockerfile
FROM busybox:latest
ENV FOO bar
vagrant@packer-debian-7:~/i$ docker build -q .
[…]
Successfully built e2363e13d2e7
vagrant@packer-debian-7:~/i$ docker inspect -f 'id:{{.id}} Id:{{.Id}} DockerVersion:{{.DockerVersion}}' e2363e13d2e7
id:<no value> Id:e2363e13d2e738843ecbe85bdd23b8d3b89f1bbba6d5ba24b1cb91294bc4f895 DockerVersion:1.0.0
vagrant@packer-debian-7:~/i$ docker save e2363e13d2e7 > e2363e13d2e7.tar
vagrant@packer-debian-7:~/i$ tar -xf e2363e13d2e7.tar -O e2363e13d2e7/json | json_pp | grep DockerVersion
   "DockerVersion" : "1.0.0",
vagrant@packer-debian-7:~/i$ docker rmi e2363e13d2e7
Deleted: e2363e13d2e738843ecbe85bdd23b8d3b89f1bbba6d5ba24b1cb91294bc4f895
vagrant@packer-debian-7:~/i$ docker load < e2363e13d2e7.tar
vagrant@packer-debian-7:~/i$ docker inspect -f 'id:{{.id}} Id:{{.Id}} DockerVersion:{{.DockerVersion}}' e2363e13d2e7
id:<no value> Id:e2363e13d2e738843ecbe85bdd23b8d3b89f1bbba6d5ba24b1cb91294bc4f895 DockerVersion:
vagrant@packer-debian-7:~/i$ docker inspect -f 'DockerVersion:{{printf "%q" .DockerVersion}}' e2363e13d2e7
DockerVersion:""

Version info:

vagrant@packer-debian-7:~/i$ uname -a
Linux packer-debian-7 3.14-0.bpo.1-amd64 #1 SMP Debian 3.14.5-1~bpo70+1 (2014-06-05) x86_64 GNU/Linux
vagrant@packer-debian-7:~/i$ docker version
Client version: 1.0.0
Client API version: 1.12
Go version (client): go1.2.1
Git commit (client): 63fe64c
Server version: 1.0.0
Server API version: 1.12
Go version (server): go1.2.1
Git commit (server): 63fe64c
vagrant@packer-debian-7:~/i$ docker info
Containers: 0
Images: 41
Storage Driver: aufs
 Root Dir: /var/lib/docker/aufs
 Dirs: 41
Execution Driver: native-0.2
Kernel Version: 3.14.0-0.bpo.1-amd64
Username: 3ofcoins
Registry: [https://index.docker.io/v1/]
WARNING: No memory limit support
WARNING: No swap limit support

[vieux]

@vbatts can you take a look ?

[vbatts]

@vieux will do

[vbatts]

this is a part of the CamelCase changes 68fb7f4