404 Error on none-existent page even ENABLE_CREATING=true.

[tamano]

When Wikitten is configured under BASE_URL like http://sample.com/wiki/, user who wants to create a new pagehttp://sample.com/wiki/newpage.md, he or she would try [newpage](/newpage.md) in index.md, but the link will return 404 error because the URL is out of BASE_URL.

This design may make user confuse when they don't have enough IT literacy.
Though the typical way to create a new page is to write a link to the new page on existing page (as PukiWiki or MediaWiki suggests to do) we should change the design to make it easy understanding.