In-scope-namespaces change to XInclude

In section 4.5, add a paragraph after the third paragraph (i.e. before
"The inclusion history..."):

  Some processors may not be able to represent an element's [in-scope
  namespaces] property if it does not include bindings for all the
  prefixes bound in its parent's [in-scope namespaces].  Such
  processors MAY therefore include additional namespace bindings
  inherited from the _include parent_ in the [in-scope namespaces] of
  the _included items_.

-- Richard