Override Rails' default gem handling and replace it with Bundler

Bundler does a better job of manage dependencies and is used by default
in Rails 3 so this will move Tracks a bit closer towards a Rails 3
conversion.

config/preinitializer.rb

@@ -0,0 +1,21 @@
+begin
+  require "rubygems"
+  require "bundler"
+rescue LoadError
+  raise "Could not load the bundler gem. Install it with `gem install bundler`."
+end
+
+if Gem::Version.new(Bundler::VERSION) <= Gem::Version.new("0.9.24")
+  raise RuntimeError, "Your bundler version is too old for Rails 2.3." +
+    "Run `gem install bundler` to upgrade."
+end
+
+begin
+  # Set up load paths for all bundled gems
+  ENV["BUNDLE_GEMFILE"] = File.expand_path("../../Gemfile", __FILE__)
+  Bundler.setup
+rescue Bundler::GemNotFound
+  raise RuntimeError, "Bundler couldn't find some gems." +
+    "Did you run `bundle install`?"
+end
+