I have updated my Subversion task for Rails/rake. It handles better svn status output, and does not fail when edge Rails are checked and svn:external‘ed into vendor directory.
You don’t have merge it with Your Rakefile, just leave svn.rake in lib/tasks and it is enough – each file from this directory with .rake suffix will be treated as Rake task definition.
File can be fetched from http://nhw.pl/download/svn.rake and original entry about this task is here.