Make Vendored Rack work with Ruby 1.9.2-p0

Seemed to have no troubles with 1.9.2dev. But
with the release version, Instiki would fail to
launch, with a 

  `load_missing_constant': Rack is not missing constant Handler! (ArgumentError)

error.

vendor/plugins/rack/lib/rack.rb

@@ -36,7 +36,8 @@ module Rack
   autoload :Deflater, "rack/deflater"
   autoload :Directory, "rack/directory"
   autoload :ForwardRequest, "rack/recursive"
-  autoload :Handler, "rack/handler"
+  require "rack/handler"
+#  autoload :Handler, "rack/handler"
   autoload :Head, "rack/head"
   autoload :Lint, "rack/lint"
   autoload :Lock, "rack/lock"