Efficiency: Entity handling
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.

app/controllers/wiki_controller.rb

lib/chunks/engines.rb

lib/chunks/nowiki.rb

lib/sanitize.rb

lib/wiki_content.rb

test/unit/chunks/nowiki_test.rb

test/unit/page_renderer_test.rb