Term Vectors: support for version and version_type

I meant version with respect to the communication, like:

```java
if (in.getVersion().onOrAfter(Version.V_1_4_0)) {
    version = Versions.readVersionWithVLongForBW(in);
    versionType = VersionType.fromValue(in.readByte());
}
```

Won't this break backward compatibility between nodes otherwise (or am I missing something)?