Log Message:
Upgrade libxml2 to 2.6.6.

Changes:

2.6.6: Feb 12 2004:
   - nanohttp and nanoftp: buffer overflow error on URI parsing (Igor and
    William) reported by Yuuichi Teranishi
   - bugfixes: make test and path issues, xmlWriter attribute serialization
    (William Brack), xmlWriter indentation (William), schemas validation
    (Eric Haszlakiewicz), XInclude dictionnaries issues (William and Oleg
    Paraschenko), XInclude empty fallback (William), HTML warnings (William),
    XPointer in XInclude (William), Python namespace serialization,
    isolat1ToUTF8 bound error (Alfred Mickautsch), output of parameter
    entities in internal subset (William), internal subset bug in push mode,
    <xs:all> fix (Alexey Sarytchev)
   - Build: fix for automake-1.8 (Alexander Winston), warnings removal
    (Philip Ludlam), SOCKLEN_T detection fixes (Daniel Richard), fix
    --with-minimum configuration.
   - XInclude: allow the 2001 namespace without warning.
   - Documentation: missing example/index.html (John Fleck), version
    dependancies (John Fleck)
   - reader API: structured error reporting (Steve Ball)
   - Windows compilation: mingw, msys (Mikhail Grushinskiy), function
    prototype (Cameron Johnson), MSVC6 compiler warnings, _WINSOCKAPI_
  patch
   - Parsers: added xmlByteConsumed(ctxt) API to get the byte offest in
    input.