Plugin tests should include test/unit

git-svn-id: http://svn-commit.rubyonrails.org/rails/trunk@2785 5ecf4fe2-1ee6-0310-87b1-e25e094e27de

railties/lib/rails_generator/generators/components/plugin/templates/unit_test.rb

+require 'test/unit'
+
 class <%= class_name %>Test < Test::Unit::TestCase
   # Replace this with your real tests.
   def test_truth