AUI-1205 - datePicker fires selectionChange event when trigger is clicked

Hi Jon,

Attached is an update for https://issues.liferay.com/browse/AUI-1205.

Eduardo recommended coming up with a less complicated fix for this one (https://github.com/eduardolundgren/alloy-ui/pull/807).  So this time I made changes so that the event will only fire on the datepicker if there has actually been a change of dates.  It's simpler but still fixes the issue.

Please let me know if there are any issues.

Thanks!