Should not initiate a 2nd traveling action potential before prior one has completed

[phet-steele]

Error: Assertion failed: Should not initiate a 2nd traveling action potential before prior one has completed.
    at window.assertions.assertFunction (https://bayes.colorado.edu/continuous-testing/snapshot-1499269170198/assert/js/assert.js:21:13)
    at AxonMembrane.initiateTravelingActionPotential (https://bayes.colorado.edu/continuous-testing/snapshot-1499269170198/neuron/js/neuron/model/AxonMembrane.js?bust=1499270412327:159:19)
    at NeuronModel.initiateStimulusPulse (https://bayes.colorado.edu/continuous-testing/snapshot-1499269170198/neuron/js/neuron/model/NeuronModel.js?bust=1499270412327:701:27)
    at listener (https://bayes.colorado.edu/continuous-testing/snapshot-1499269170198/neuron/js/neuron/view/NeuronScreenView.js?bust=1499270412327:261:47)
    at https://bayes.colorado.edu/continuous-testing/snapshot-1499269170198/sun/js/buttons/PushButtonModel.js?bust=1499270412327:168:9
    at Array.forEach (<anonymous>)
    at PushButtonModel.fire (https://bayes.colorado.edu/continuous-testing/snapshot-1499269170198/sun/js/buttons/PushButtonModel.js?bust=1499270412327:167:12)
    at Array.<anonymous> (https://bayes.colorado.edu/continuous-testing/snapshot-1499269170198/sun/js/buttons/PushButtonModel.js?bust=1499270412327:102:16)
    at Emitter.emit2 (https://bayes.colorado.edu/continuous-testing/snapshot-1499269170198/axon/js/Emitter.js?bust=1499270412327:147:49)
    at Property._notifyObservers (https://bayes.colorado.edu/continuous-testing/snapshot-1499269170198/axon/js/Property.js?bust=1499270412327:207:29)
Approximately 7/5/2017, 9:39:30 AM

[jonathanolson]

Looks potentially related to the de-PropertySet-ification.

[Denz1994]

I can no longer initiate a second stimulus without the completion of the first. Closing this issue because it was reviewed with @jbphet.