* Fixes for issue with captcha image not showing up on windows servers in some cases.
* Changes to make sure the captcha image is showed correctly when hn_captcha is used
and $_SERVER['DOCUMENT_ROOT'] is not set correctly.
* Removed support for the b2evo library. It is derived from hn_captcha and doesn't offer
any extra functionality.
* Use an unmodified version of the hn_captcha library (only kept some spelling fixes).