Include the current machine identifier when creating Access Tokens

Previously, the description for the token was simply "hub". Now, it's:

    hub for {USER}@{HOSTNAME}

This reduces the chance of token name collisions when the same user uses
hub to authenticate from different machines, as well as serves as
information to distinguish between various tokens in user's Personal
Acess Token list.

features/authentication.feature

@@ -5,10 +5,14 @@ Feature: OAuth authentication
   Scenario: Ask for username & password, create authorization
     Given the GitHub API server:
       """
+      require 'socket'
+      require 'etc'
+      machine_id = "#{Etc.getlogin}@#{Socket.gethostname}"
+
       post('/authorizations') {
         assert_basic_auth 'mislav', 'kitty'
         assert :scopes => ['repo'],
-               :note => 'hub',
+               :note => "hub for #{machine_id}",
                :note_url => 'http://hub.github.com/'
         json :token => 'OTOKEN'
       }

lib/hub/github_api.rb

@@ -337,7 +337,7 @@ module Hub
         auth_url = URI.parse("https://%s@%s/authorizations" % [CGI.escape(user), host])
         auth_params = {
           :scopes => ['repo'],
-          :note => 'hub',
+          :note => "hub for #{local_user}@#{local_hostname}",
           :note_url => oauth_app_url
         }
         res = nil
@@ -359,6 +359,16 @@ module Hub
 
         res.data['token']
       end
+
+      def local_user
+        require 'etc'
+        Etc.getlogin
+      end
+
+      def local_hostname
+        require 'socket'
+        Socket.gethostname
+      end
     end
 
     module GistAuth