* Adds one sequence feature to the store, and returns true, unless the
* feature is already contained in the store, in which case this method
* returns false. Containment is determined by SequenceFeature.equals()
* Adds one sequence feature to the store, and returns true, unless the
* feature is already contained in the store, in which case this method
* returns false. Containment is determined by SequenceFeature.equals()