Add zebra striping to guestbook entries

Having alternating guestbook entries tagged with even and odd would really help in styling the posts. I have created a patch that adds this ability. It appears to work fine on my system.

I have also included in this patch, a fix for the include_once of spam module, as it only looks in two places. The method I used finds out where spam is installed and uses that path, no matter where it is.