+/**
+ * Constructs a new ClockVector, given a parent ClockVector and a first
+ * ModelAction. This constructor can assign appropriate default settings if no
+ * parent and/or action is supplied.
+ * @param parent is the previous ClockVector to inherit (i.e., clock from the
+ * same thread or the parent that created this thread)
+ * @param act is an action with which to update the ClockVector
+ */