ensure that the 'previous' object in 'change' events contains the original (or, most recent) values for all properties of the record (for known attributes)

Enyo-DCO-1.1-Signed-off-by: Cole Davis <cole.davis@lge.com>
Merge pull request #467 from enyojs/ENYO-3125-cole-davis

Fix for ENYO-3125

Reviewed-By: Ben Combee (ben.combee@lge.com)