[IronPython] pyexpat for IronPython update

[Sanghyeon Seo]

I made some updates to pyexpat.py.
http://sparcs.kaist.ac.kr/~tinuviel/fepy/lib/

* Support for XML namespaces
It can now read NamespaceURI + LocalName instead of Name.

* Code simplification
It should be a bit easier to read now. Used StringReader instead of
MemoryStream.

Seo Sanghyeon