engine.Env.Expand applies shell-style variable expansion on an input string
engine.Env.Add: append multiple values for the same key
(squash) unit test for engine.Env.Expand
(squash) nicer implementation of dockerfile.ParseScript and ParseExpr
pkg/dockerfile.ReflectorHandler: gracefully ignore unknown instructions (and print a warning)
engine.Env.ToScript returns a text representation of the env in Dockerfile syntax
(squash) use new ReflectorHandler API
runconfig.Config.CmdEnv: reuse engine.Env.Expand
runconfig.Config.AsScript returns a text representation of the Config in the Dockerfile syntax
expose runconfig.ParseArgCommand