[SAC] mantra requirement removed

I've restored the user registration so it doesn't ask for
a mantra anymore. Shall you see unexpected activities
putting it back is simple:

www# cd /usr/lib/cgi-bin; mv MAINTAINANCE.example MAINTAINANCE

Let's see how it goes.

Note that the form was not improved so there's still no
email confirmation or password reset.

There's still an hourly cronjob on the tracsvn machine
that should send an email here if more than 5 users
register within an hour.