We need support for IsBoolFlag() in order to implement `--version`
(without an explicit `--version=true`) and also `--version=raw`.

Updated using `godep update github.com/spf13/pflag`.

Tested:
  $ _output/local/bin/linux/amd64/kubelet --version
  Kubernetes v0.8.0-590-gc61720437ec181
  $ _output/local/bin/linux/amd64/kubelet --version=raw
  version.Info{Major:"0", Minor:"8+", GitVersion:"v0.8.0-590-gc61720437ec181", GitCommit:"c61720437ec181ae3fbbfb9d6df5efdf3e3b6c2e", GitTreeState:"clean"}