[css] [bug] :not arguments

[Bjoern H. <der...@gm...>]

Hi,

  :not() allows only a simple selector as argument but CSS::SAC
represents this incorrectly, e.g. it considers

  :not(:first-child)

to be equivalent to

  :not(*:first-child)

while it is not. The argument is either a ELEMENT_NODE_SELECTOR or a
Condition != AND_CONDITION (based on supported conditions, i.e.,
OR_CONDITION would probably also be invalid but we don't have
OR_CONDITIONs in CSS3).