Previously, used a regexp to find and convert named entities in the content.
Now use a more efficient algorithm.
Similar tweak for converting NCRs before checking whether text is valid utf-8.
The URIChunk and LocalURICunk handlers were
1) Slow
2) Buggy (prone to produce ill-formed pages in edge cases)
3) Of dubious utility
So I ditched them. No auto-linked URLs, but who cares?
