captcha 6.x-2.0-beta1

First Beta of a rework of the CAPTCHA module, that does not require sessions for storing the challenge solutions, but uses a dedicated table instead.

The use of sessions in the previous versions of the CAPTCHA module is responsible for a large volume of support requests in the issue queue, because of problems with sessions, "user 0", cookies, browser security levels, etc.
Dropping the sessions requirement should eradicate this type of problems.