add verbose output to rails startup if RAILS_VERBOSE_STARTUP env is true

Once you have lots of gems and plugins and routes start can take a long time. It helps a lot to see verbose output of what is taking so long. This patch file make rails show nice output like:

                   starting 0.0000
         check_ruby_version 0.0016
     install_gem_spec_stubs 0.0016
              set_load_path 0.0006
         add_gem_load_paths 0.0330
                         ============== REQUIRE FRAMEWORKS =================
                                              active_record 0.0107
                                          action_controller 0.0023
                                                action_view 0.0023
                                              action_mailer 0.2798
                                            active_resource 0.3606
         set_autoload_paths 0.0001
      add_plugin_load_paths 0.1356
           load_environment 0.0736
         preload_frameworks 0.0000
        initialize_encoding 0.0000
        initialize_database 0.3531
           initialize_cache 0.0059
initialize_framework_caches 0.1401
          initialize_logger 0.0019

initialize_framework_logging 0.0001 initialize_dependency_mechanism 0.0000

      initialize_whiny_nils 0.0035
       initialize_time_zone 0.0000
            initialize_i18n 0.0000

initialize_framework_settings 0.0002

 initialize_framework_views 0.0017
           initialize_metal 0.0148
     add_support_load_paths 0.0000

etc.

if the env var RAILS_VERBOSE_STARTUP is set.