After vendor/plugins were removed from rails, the new method to create
plugins is to create gem plugins. Most of the time if you create a
new plugin in rails application's directory, you want to extract
something from that application and use it immediately, ie. add
such line to Gemfile:

  gem 'foo', :path => './vendor/foo'

This commit makes plugin new generator to add such line automatically.

ruby 1.9 related refactoring

get rid of using instance_variable_names method from AS

- instance_variables return symbols in 1.9
- there is instance_variable_defined? method

use stub instead of redefining method to suppress warnings

if turn available then MiniTest::Unit.respond_to?(:use_natural_language_...

Fixed after_initialize callbacks call on AR model #dup

add benchmark helper that works in erb

Remove more references to Test::Unit

all tests pass, not the number of tests.

Array.wrap is an overhead as there is already check for class

revert "fixing some tests on ruby 1.9.3" 

removed unnecessary require for activesupport/core_ext/array/wrap