ENYO-2020: Adjusted version of Chris VanHoover's fix for mismatched popup hiding by having the stack not simply pop items, but instead search to remove the proper item, then put focus on the last one left.

Test case has been added in separate commit to onyx Popup sample.

Enyo-DCO-1.1-Signed-Off-By: Ben Combee (ben.combee@lge.com)
Update comment for enyo.dispatcher.release() based on Mark's observation that it was out of date

Enyo-DCO-1.1-Signed-Off-By: Ben Combee (ben.combee@lge.com)