fixed apibuild.py's generation of "constructors" to be in alphabetical

* doc/apibuild.py, doc/APIconstructors.html, doc/libxml2-refs.xml,
  win32/libxml2.def.src: fixed apibuild.py's generation of
  "constructors" to be in alphabetical order (instead of previous
  random sequence); regenerated resulting files.
5 files changed