* xmlschemas.c xmlschemastypes.c: Fixed xs:boolean to reject
  the empty string (reported by Bas Driessen on the mailing-list).
  Fixed schema XSI-acquisition and construction: the schemata
  (xmlSchema) didn't get the targetNamespace in some cases, thus
  the component resolution mechanism failed to work. The XSI
  stuff needs to be tested more intensively; think about how
  to test this for regression.