Update Rails, rails_xss and Bundler

Update Bundler to 1.0.15.
Update Rails to 2.3.12.
Update rails_xss plugin.

The latter two were the
source of a considerable
amount of grief, as rails_xss
is now MUCH stricter about what
string methods can be used.

Also made it possible to use
rake 0.9.x with Instiki. But
you probably REALLY want to use

 ruby bundle exec rake ...

instead of just saying

 rake ....

vendor/rails/railties/lib/tasks/framework.rake

@@ -24,7 +24,7 @@ namespace :rails do
       begin
         chdir("vendor/rails") do
           rails.dependencies.select { |g| deps.include? g.name }.each do |g|
-            Gem::GemRunner.new.run(["unpack", g.name, "--version", g.version_requirements.to_s])
+            Gem::GemRunner.new.run(["unpack", g.name, "--version", g.respond_to?(:requirement) ? g.requirement.to_s : g.version_requirements.to_s])
             mv(Dir.glob("#{g.name}*").first, g.name)
           end