* xmlschemas.c: Added validation for the attribute "id" in the
  schemata; doing this needed error report fixes for notations,
  facets and group. Changed NOTATION validation to work with the
  declared NOTATIONs in the schema; this does have no impact on
  the validation via the relaxng module.
* xmlschemastypes.c include/libxml/xmlschemastypes.h:
  Added xmlSchemaNewNOTATIONValue to the API to be able to do
  the NOTATION validation described above.
* test/schemas/element-err_0.xsd test/schemas/annot-err_0.xsd:
  Fixed the values of the "id" attributes, which were not validated
  previously.