Sync with latest Instiki trunk. Changes:

1) Upgrade Rails to 1.2.3
2) Revert RedCloth to previous version (who %#$@ cares?)
3) Preserve the Rails Security fix  to vendor/rails/actionpack/lib/action_controller/caching.rb from Revision 80.

vendor/rails/railties/lib/commands/plugin.rb

@@ -240,11 +240,12 @@ class Plugin
     def install_using_http(options = {})
       root = rails_env.root
       mkdir_p "#{root}/vendor/plugins"
-      Dir.chdir "#{root}/vendor/plugins"
-      puts "fetching from '#{uri}'" if $verbose
-      fetcher = RecursiveHTTPFetcher.new(uri)
-      fetcher.quiet = true if options[:quiet]
-      fetcher.fetch
+      Dir.chdir "#{root}/vendor/plugins" do
+        puts "fetching from '#{uri}'" if $verbose
+        fetcher = RecursiveHTTPFetcher.new(uri)
+        fetcher.quiet = true if options[:quiet]
+        fetcher.fetch
+      end
     end
 
     def svn_command(cmd, options = {})