GF-61237: Calling super method for transitionEnd only when the originator is moon.Popup
Fixing http://jira2.lgsvl.com/browse/GF-61237

Reproduce:
1) Run moon.Popup sample and set animate: false on panel popup.
2) Click "panel in popup" button to open popup.
3) Click paging control to scroll down.
4) Tap on outside of panel to hide.
5) Tap on other buttons.

Problem:
Buttons are not getting tap event.

When the popup has components which is fires ontransitionend event, the popup is calling showingChanged handler of enyo.Popup which is captures events.

Solution:
Check originator for transitionEnd event.

DCO-1.1-Signed-Off-By: Kunmyon Choi <kunmyon.choi@lge.com>
Add missing return on super call of getShowing on moon.Popup

DCO-1.1-Signed-Off-By: Kunmyon Choi <kunmyon.choi@lge.com>
Check for null case of current focus on showingChanged of moon.Popup

DCO-1.1-Signed-Off-By: Kunmyon Choi <kunmyon.choi@lge.com>
GF-61237: Simplify falsy-check logic.
DCO-1.1-Signed-Off-By: Kevin Schaaf <kevin.schaaf@lge.com>
Merge pull request #1125 from enyojs/GF-61237-kunmyonchoi

GF-61237: Calling super method for transitionEnd only when the originator is moon.Popup