API, issue 1471: Allow users belonging to the docker group to use the docker client
Revert "docker.upstart: avoid spawning a `sh` process"

This reverts commit 24dd50490a027f01ea086eb90663d53348fa770e.
Make sure ENV instruction within build perform a commit each time
Handle ip route showing mask-less IP addresses

Sometimes `ip route` will show mask-less IPs, so net.ParseCIDR will fail. If it does we check if we can net.ParseIP, and fail only if we can't.
Fixes #1214
Fixes #362
Bump to 0.5.3
Add hostname to the container environment.
Fix TestEnv
Update changelog to include hostname commit
Merge pull request #1510 from dotcloud/bump_0.5.3

Bump to 0.5.3