Support rspec 3.0+ out of the box

Rspec 3.0 introduces separate _helper files for full tests and tests that
don't require the full rails app to be loaded. Because of this and because
the point of zeus is to pre-load your app, default to loading the full
rails_helper for zeus. You can override this behavior with the env var
RAILS_TEST_HELPER.

Fixes #474

rubygem/lib/zeus/rails.rb

@@ -191,7 +191,11 @@ def test_helper
       if ENV['RAILS_TEST_HELPER']
         require ENV['RAILS_TEST_HELPER']
       else
-        if File.exists?(ROOT_PATH + "/spec/spec_helper.rb")
+        if File.exists?(ROOT_PATH + "/spec/rails_helper.rb")
+          # RSpec >= 3.0+
+          require 'rails_helper'
+        elsif File.exists?(ROOT_PATH + "/spec/spec_helper.rb")
+          # RSpec < 3.0
           require 'spec_helper'
         elsif File.exists?(ROOT_PATH + "/test/minitest_helper.rb")
           require 'minitest_helper'

rubygem/spec/rails_spec.rb

@@ -17,7 +17,16 @@ module Zeus
         ENV.clear
       end
 
+      it "requires rails_helper when using rspec 3.0+" do
+        mock_file_existence(ROOT_PATH + "/spec/rails_helper.rb", true)
+
+        rails.should_receive(:require).with("rails_helper")
+
+        rails.test_helper
+      end
+
       it "when spec_helper exists spec_helper is required" do
+        mock_file_existence(ROOT_PATH + "/spec/rails_helper.rb", false)
         mock_file_existence(ROOT_PATH + "/spec/spec_helper.rb", true)
 
         rails.should_receive(:require).with("spec_helper")
@@ -26,6 +35,7 @@ module Zeus
       end
 
       it "when minitest_helper exists minitest_helper is required" do
+        mock_file_existence(ROOT_PATH + "/spec/rails_helper.rb", false)
         mock_file_existence(ROOT_PATH + "/spec/spec_helper.rb", false)
         mock_file_existence(ROOT_PATH + "/test/minitest_helper.rb", true)
 
@@ -34,7 +44,8 @@ module Zeus
         rails.test_helper
       end
 
-      it "when there is no spec_helper or minitest_helper, test_helper is required" do
+      it "when there is no rspec helpers or minitest_helper, test_helper is required" do
+        mock_file_existence(ROOT_PATH + "/spec/rails_helper.rb", false)
         mock_file_existence(ROOT_PATH + "/spec/spec_helper.rb", false)
         mock_file_existence(ROOT_PATH + "/test/minitest_helper.rb", false)