Log Message:
update to libxml2-2.6.15

changes:

* security fixes on the nanoftp and nanohttp modules
For details see:
http://www.securityfocus.com/archive/1/379383/2004-10-24/2004-10-30/0

* build fixes:
  - xmllint detection bug in configure
  - building outside the source tree (Thomas Fitzsimmons)
* bug fixes:
  - HTML parser on broken ASCII chars in names (William)
  - Python paths (Malcolm Tredinnick)
  - xmlHasNsProp and default namespace (William)
  - saving to python file objects (Malcolm Tredinnick)
  - DTD lookup fix (Malcolm)
  - save back <group> in catalogs (William)
  - tree build fixes (DV and Rob Richards)
  - Schemas memory bug
  - structured error handler on Python 64bits
  - thread local memory deallocation
  - memory leak reported by Volker Roth
  - xmlValidateDtd in the presence of an internal subset
  - entities and _private problem (William)
  - xmlBuildRelativeURI error (William).
* improvements:
  - better XInclude error reports (William)
  - tree debugging module and tests
  - convenience functions at the Reader API (Graham Bennett)
  - add support for PI in the HTML parser.

Update BUILDLINK_RECOMMENDED to 2.6.15 for the security fix.