Implemented Module#module_exec for ruby 1.8.6. This is needed for the…

… shared example group parameter feature to work.

This is based on the implementations in rubinius and backports:
- http://github.com/marcandre/backports/blob/v1.18.1/lib/backports/1.8.7/module.rb
- http://github.com/evanphx/rubinius/blob/release-1.0.1/kernel/common/module.rb#L438-441

lib/rspec/core.rb

@@ -1,5 +1,6 @@
 require 'rspec/core/kernel_extensions'
 require 'rspec/core/object_extensions'
+require 'rspec/core/module_extensions'
 require 'rspec/core/load_path'
 require 'rspec/core/deprecation'
 require 'rspec/core/reporter'

lib/rspec/core/module_extensions.rb

@@ -0,0 +1,16 @@
+module RSpec
+  module Core
+    module ModuleExtensions
+      unless respond_to?(:module_exec)
+        def module_exec(*args, &prc)
+          instance_exec(*args, &prc)
+        end
+        alias_method :class_exec, :module_exec
+      end
+    end
+  end
+end
+
+class Module
+  include RSpec::Core::ModuleExtensions
+end