- Cleaned up, improved comments

- Cleaned up, improved comments
- Unified all possible interceptors (CGI,
  block, trust, fast_redirect) in one
  place, with one (CGI) answer generation
  mechansim. Much clearer now.
- Removed the GIF image generation, which
  is now done in filters.c:block_url()
- Made error conditions like domain lookup
  failiure or (various) problems while talking
  to the server use cgi.c:error_response()
  instead of generating HTML/HTTP in chat() (yuck!)
- Removed logentry from cancelled commit