Simplify how the expect_with configuration works.

- There's no need to include RSpec::Matchers or Test::Unit::Assertions into an adapter module when we can just include them directly.
- It makes it possible to interrogate @expectation_frameworks to see what was already configured and included.  Before, @expectation_frameworks contained [RSpec::Core::ExpectationFrameworkAdapter], regardless of what was configured.

lib/rspec/core/configuration.rb

@@ -223,18 +223,22 @@ def expectation_framework=(framework)
       def expect_with(*frameworks)
         assert_no_example_groups_defined(:expect_with)
         @expectation_frameworks.clear
-        frameworks.each do |framework|
+
+        modules = frameworks.map do |framework|
           case framework
           when :rspec
-            require 'rspec/core/expecting/with_rspec'
+            require 'rspec/expectations'
             self.expecting_with_rspec = true
+            ::RSpec::Matchers
           when :stdlib
-            require 'rspec/core/expecting/with_stdlib'
+            require 'test/unit/assertions'
+            ::Test::Unit::Assertions
           else
             raise ArgumentError, "#{framework.inspect} is not supported"
           end
-          @expectation_frameworks << RSpec::Core::ExpectationFrameworkAdapter
         end
+
+        @expectation_frameworks.push(*modules)
       end
 
       def full_backtrace=(true_or_false)

spec/rspec/core/configuration_spec.rb

@@ -1,6 +1,9 @@
 require 'spec_helper'
 require 'tmpdir'
 
+# so the stdlib module is available...
+module Test; module Unit; module Assertions; end; end; end
+
 module RSpec::Core
 
   describe Configuration do
@@ -91,7 +94,7 @@ module RSpec::Core
 
     describe "#expectation_framework" do
       it "defaults to :rspec" do
-        config.should_receive(:require).with('rspec/core/expecting/with_rspec')
+        config.should_receive(:require).with('rspec/expectations')
         config.expectation_frameworks
       end
     end
@@ -104,10 +107,13 @@ module RSpec::Core
     end
 
     describe "#expect_with" do
-      [:rspec, :stdlib].each do |framework|
+      [
+        [:rspec,  'rspec/expectations'],
+        [:stdlib, 'test/unit/assertions']
+      ].each do |(framework, required_file)|
         context "with #{framework}" do
-          it "requires the adapter for #{framework.inspect}" do
-            config.should_receive(:require).with("rspec/core/expecting/with_#{framework}")
+          it "requires #{required_file}" do
+            config.should_receive(:require).with(required_file)
             config.expect_with framework
           end
         end