ENYO-2229: modify enyo.dom.getComputedBoxValue with workaround for IE8

Enyo-DCO-1.1-Signed-Off-By: Ben Combee (ben.combee@lge.com)
Merge pull request #383 from enyojs/ENYO-2229-unwiredben

ENYO-2229: modify enyo.dom.getComputedBoxValue with workaround for IE8