[css] swallow the ancestor selector
[css] swallow the ancestor selector

Handle ancestor selector to ensure an incomplete selector does not get
applied to the wrong node.

pwithnall/mx,clutter-project/mx,jonnylamb/mx,jonnylamb/mx,clutter-project/mx,clutter-project/mx,jonnylamb/mx,pwithnall/mx,pwithnall/mx,pwithnall/mx,jonnylamb/mx,clutter-project/mx