Log Message:
Update to 2.5.6:
2.5.6: Apr 1 2003:
   - Fixed W3C XML Schemas datatype, should be compliant now except for
    binHex and base64 which are not supported yet.
   - bug fixes: non-ASCII IDs, HTML output, XInclude on large docs and
    XInclude entities handling, encoding detection on external subsets, XML
    Schemas bugs and memory leaks, HTML parser (James Bursa)
   - portability: python/trio (Albert Chin), Sun compiler warnings
   - documentation: added --relaxng option to xmllint man page (John)
   - improved error reporting: xml:space, start/end tag mismatches, Relax NG
    errors