Issue 463: Provide a signout\logout method

Src/GoogleApis.Auth.WP/OAuth2/AuthorizationCodeWPInstalledApp.cs

Index: Src/GoogleApis.Auth.WP/OAuth2/AuthorizationCodeWPInstalledApp.cs
===================================================================
--- a/Src/GoogleApis.Auth.WP/OAuth2/AuthorizationCodeWPInstalledApp.cs
 b/Src/GoogleApis.Auth.WP/OAuth2/AuthorizationCodeWPInstalledApp.cs
@@ -38,14 38,25 @@
 {
 private readonly IAuthorizationCodeInstalledApp innerInstallApp;
- /// <summary>Constructs a new authorization code installed application for WP.</summary>
- /// <param name="authorizationCodeFlowInitializer">A authorization code flow initializer.</param>
 /// <summary>
 /// Constructs a new authorization code for Windows Phone targeting an installed application flow.
 /// </summary>
 /// <param name="authorizationCodeFlowInitializer">An authorization code flow initializer.</param>
 public AuthorizationCodeWPInstalledApp(AuthorizationCodeFlow.Initializer authorizationCodeFlowInitializer)
 {
 var flow = new AuthorizationCodeFlow(authorizationCodeFlowInitializer);
 innerInstallApp = new AuthorizationCodeInstalledApp(flow, new AuthorizationCodeBroker());
 }
 /// <summary>
 /// Constructs a new authorization code for Windows Phone targeting an installed application flow.
 /// </summary>
 /// <param name="flow">An authorization code flow.</param>
 public AuthorizationCodeWPInstalledApp(IAuthorizationCodeFlow flow)
 {
 innerInstallApp = new AuthorizationCodeInstalledApp(flow, new AuthorizationCodeBroker());
 }
 #region IAuthorizationCodeInstalledApp Members
 public IAuthorizationCodeFlow Flow