platform switch test

Rakefile

@@ -1,2 +1,18 @@
 require 'bundler'
 Bundler::GemHelper.install_tasks
+
+namespace :spec do
+  desc "Run on three Rubies"
+  task :platforms do
+    current = %x{rvm-prompt v}
+    
+    %w{1.8.7 1.9.2 ree}.each do |version|
+      puts "Switching to #{version}"
+      system %{rvm #{version}}
+      system %{bundle exec rspec spec}
+      break if $?.exitstatus != 0
+    end
+
+    system %{rvm #{current}}
+  end
+end