ensure that the length property is updated when using empty

Enyo-DCO-1.1-Signed-Off-By: Cole Davis (cole.davis@lge.com)
ensure that mixins can still apply additional mixins

Enyo-DCO-1.1-Signed-Off-By: Cole Davis (cole.davis@lge.com)
initial testing
ENYO-42: [Garnet] drag event occurs when multi touch
Enyo-DCO-1.1-Signed-off-by: Krishna Rangarajan <krishna.rangarajan@lge.com>
Update version string to 2.5.1-pre.5