* xmlschemas.c: Fixed comparison for default/fixed attribute
  values, if the type was 'xsd:string'. Changed the comparison
  for IDCs to use the whitespace aware comparison function.
* xmlschemastypes.c include/libxml/xmlschemastypes.h:
  Added xmlSchemaGetCanonValue, xmlSchemaNewStringValue and
  xmlSchemaCompareValuesWhtsp to the API. Added functions
  to compare strings with whitespace combinations of "preserve",
  "replace" and "collapse".