Fixes theme discovery under JRuby on Rails war structure (#632, #5404).

git-svn-id: svn+ssh://rubyforge.org/var/svn/redmine/trunk@3710 e93f8b46-1217-0410-a6f0-8f06a7374b81

lib/redmine/themes.rb

@@ -54,7 +54,7 @@ module Redmine
     private
         
     def self.scan_themes
-      dirs = Dir.glob("#{RAILS_ROOT}/public/themes/*").select do |f|
+      dirs = Dir.glob("#{Rails.public_path}/themes/*").select do |f|
         # A theme should at least override application.css
         File.directory?(f) && File.exist?("#{f}/stylesheets/application.css")
       end