Revert "Remove at_exit hook and rspec/autorun"

This reverts commit c6f7806.

- needed to revert because this broke the rake task with rcov

bin/rspec

@@ -1,3 +1,2 @@
 #!/usr/bin/env ruby
-require 'rspec/core'
-exit RSpec::Core::Runner.run(ARGV, $stderr, $stdout)
+require 'rspec/autorun'

lib/rspec/autorun.rb

@@ -0,0 +1,2 @@
+require 'rspec/core'
+RSpec::Core::Runner.autorun

lib/rspec/core/example_group.rb

@@ -20,6 +20,7 @@ def self.world
       end
 
       def self.inherited(klass)
+        RSpec::Core::Runner.autorun
         world.example_groups << klass if klass.top_level?
       end
 

lib/rspec/core/runner.rb

@@ -4,8 +4,27 @@ module RSpec
   module Core
     class Runner
 
+      def self.autorun
+        return if autorun_disabled? || installed_at_exit? || running_in_drb?
+        @installed_at_exit = true
+        at_exit { run(ARGV, $stderr, $stdout) ? exit(0) : exit(1) }
+      end
+
+      def self.autorun_disabled?
+        @autorun_disabled ||= false
+      end
+
       def self.disable_autorun!
-        RSpec.deprecate("disable_autorun!")
+        @autorun_disabled = true
+      end
+
+      def self.installed_at_exit?
+        @installed_at_exit ||= false
+      end
+
+      def self.running_in_drb?
+        (DRb.current_server rescue false) &&
+        !!((DRb.current_server.uri) =~ /druby\:\/\/127.0.0.1\:/)
       end
 
       def self.trap_interrupt

spec/rspec/core/runner_spec.rb

@@ -2,6 +2,24 @@
 
 module RSpec::Core
   describe Runner do
+    describe 'at_exit' do
+      it 'sets an at_exit hook if none is already set' do
+        RSpec::Core::Runner.stub(:installed_at_exit?).and_return(false)
+        RSpec::Core::Runner.stub(:running_in_drb?).and_return(false)
+        RSpec::Core::Runner.stub(:at_exit_hook_disabled?).and_return(false)
+        RSpec::Core::Runner.should_receive(:at_exit)
+        RSpec::Core::Runner.autorun
+      end
+
+      it 'does not set the at_exit hook if it is already set' do
+        RSpec::Core::Runner.stub(:installed_at_exit?).and_return(true)
+        RSpec::Core::Runner.stub(:running_in_drb?).and_return(false)
+        RSpec::Core::Runner.stub(:at_exit_hook_disabled?).and_return(false)
+        RSpec::Core::Runner.should_receive(:at_exit).never
+        RSpec::Core::Runner.autorun
+      end
+    end
+
     describe "#run" do
       context "with --drb or -X" do
         before(:each) do