Make download_binaries_tests work on OS X: it's normal that helper-sc…

…ripts/download_binaries/extconf.rb cannot find Ruby extensions for OS X

test/integration_tests/downloaded_binaries_tests.rb

@@ -29,6 +29,7 @@
 $LOAD_PATH.unshift("#{source_root}/lib")
 require 'phusion_passenger'
 PhusionPassenger.locate_directories
+PhusionPassenger.require_passenger_lib 'platform_info/operating_system'
 require 'tmpdir'
 require 'fileutils'
 require 'webrick'
@@ -132,7 +133,7 @@ def start_server(document_root)
 			File.rename("download_cache.old", "download_cache")
 			server.stop
 		end
-	end
+	end if PlatformInfo.os_name == "linux"
 
 	specify "helper-scripts/download_binaries/extconf.rb fails at downloading all necessary binaries if one of them does not exist" do
 		FileUtils.mkdir_p("server_root")