[PATCH] Implement spamming mitigations for comments

[Jelle van der Waa]

This is an attempt to mitigate the spam flood which has targeted
aur.archlinux.org in a simple and (hopefully) effective way. As
described in the commit message it just adds a hidden field which these
automated bots fill in to make the form submission look "valid" for
normal users nothing changes.

I also created a patch for account registration, but that patch is a bit
bigger and I'm not sure if these automated bot setups are smart enough
to report that registration fails although one can argue that they can
detect if a comment was 'submitted'. Either way the comment patch has
the smallest impact codewise and is an easy way to figure out if it
works.

Greetings,

Jelle van der Waa