Add #add_should_and_should_not to configuration API.

This allows users to manually add these methods to proxy objects that do not have them.

Closes #114.

lib/rspec/matchers/configuration.rb

@@ -38,6 +38,19 @@ def syntax
         syntaxes << :expect if Expectations::Syntax.expect_enabled?
         syntaxes
       end
+
+      # Adds `should` and `should_not` to the given classes
+      # or modules. This can be used to ensure `should` works
+      # properly on things like proxy objects (particular
+      # `Delegator`-subclassed objects on 1.8).
+      #
+      # @param [Array<Module>] modules the list of classes or modules
+      #   to add `should` and `should_not` to.
+      def add_should_and_should_not_to(*modules)
+        modules.each do |mod|
+          Expectations::Syntax.enable_should(mod)
+        end
+      end
     end
 
     # The configuration object

spec/rspec/matchers/configuration_spec.rb

@@ -1,4 +1,5 @@
 require 'spec_helper'
+require 'delegate'
 
 module RSpec
   module Matchers
@@ -7,6 +8,24 @@ module Matchers
         RSpec::Matchers.configuration.should be_a(RSpec::Matchers::Configuration)
         RSpec::Matchers.configuration.should be(RSpec::Matchers.configuration)
       end
+
+      context 'on an interpreter that does not provide BasicObject', :unless => defined?(::BasicObject) do
+        before { RSpec::Expectations::Syntax.disable_should(Delegator) }
+
+        let(:klass) do
+          Class.new(SimpleDelegator) do
+            def delegated?; true; end
+          end
+        end
+
+        let(:instance) { klass.new(Object.new) }
+
+        it 'provides a means to manually add it Delegator' do
+          instance.should_not respond_to(:delegated?) # because #should is being delegated...
+          RSpec::Matchers.configuration.add_should_and_should_not_to Delegator
+          instance.should respond_to(:delegated?) # now it should work!
+        end
+      end
     end
 
     shared_examples_for "configuring the expectation syntax" do