Filter registration requests for spam

[ear1grey]

Registration spam is becoming a problem. bbpress should provide the same spam protection for registration as it does for actual messages.

See also: http://bbpress.org/forums/topic/539

Akismet should already be doing this. It should mark as bozos any account it thinks is a spam registration.

That's good news, thanks.

In which case the UI needs to provide some kind of feedback so that false-positives can be caught and avoided, and false-negatives can be submitted back to Akismet.

Let's call the UI a dupe of #530.