Until I have my tumblr tumblog themed and they add some nice code posting facilities, here’s a nice snippet for you all.
Detect whether any files on the SVN server have been changed in a more recent revision (i.e. something like CC.rb should rebuild your project):
require 'rexml/document'
REXML::Document.new(`svn status -u --xml`).elements.to_a("//entry//repos-status").any?