~LLEventPumps() deletes every LLEventPump instance it created itself. However,
many classes themselves contain LLEventPump subclass instances. These are
registered with LLEventPumps without it managing their lifespan.

But LLEventPump::reset() frees the LLStandardSignal aka
boost::signals2::signal instance owned by the LLEventPump, perforce
disconnecting all current listeners and disabling the LLEventPump. Even though
the instance still exists, if someone subsequently calls post(), nothing will
happen -- which is better than control trying to reach a method of a deleted
object.