If the boundBehavior prevents the flickable from moving its content
item in response to a drag it shouldn't grab the mouse as that will
prevent a parent MouseArea or Flickable from handling the drag.

Task-number: QTBUG-29718
Change-Id: I3a1be4ed0132b91dca2fb0387ecefd39275a52da
Reviewed-by: Alan Alpert <aalpert@rim.com>