ContextLink TVs are not kept in sync with those in CompositeTVs

[ferrouswheel]

When ContextLinks are added, they also add a VersionHandle to the associated CompositeTruthValues. However, if the ContextLink or VersionHandle TV is changed, then the TVs in each of these get out of sync. It should not be up to client code to maintain both TVs as this will surely result in a mess.

I checked whether they might have cleverly shared a reference to the same TV object, but they don't. The TV reference passed to
CompositeTruthValue::setVersionedTV is cloned.

We could try to share the same TV object (more space efficient but possibly more difficult), or we could add code that watches for TV
changes to ContextLinks/CompositeTVs.