feat(etcd): add version flag

print the version and exit, very simple :)

Conflicts:
	etcd.go
feat(server): export ReleaseVersion

releaseVersion is needed in etcd.go to print it out in the -version
flag.
Merge pull request #242 from philips/add-version-flag-0.2

feat(etcd): add version flag
Merge branch '0.2' of https://github.com/coreos/etcd into 0.2