If the user is already logged out when they hit "sign out", do not show error.

close #630.

resources/static/shared/network.js

@@ -235,7 +235,15 @@ BrowserID.Network = (function() {
           auth_status = false;
           if (onComplete) onComplete();
         },
-        error: onFailure
+        error: function(info, xhr, textStatus) {
+          if (info.network.status === 400) {
+            auth_status = false;
+            if (onComplete) onComplete();
+          }
+          else {
+            onFailure && onFailure(info);
+          }
+        }
       });
     },
 

resources/static/test/qunit/mocks/xhr.js

@@ -61,7 +61,8 @@ BrowserID.Mocks.xhr = (function() {
       "post /wsapi/complete_user_creation invalid": { success: false },
       "post /wsapi/complete_user_creation ajaxError": undefined,
       "post /wsapi/logout valid": { success: true },
-      "post /wsapi/logout ajaxError": undefined,
+      "post /wsapi/logout not_authenticated": 400,
+      "post /wsapi/logout ajaxError": 401,
       "get /wsapi/have_email?email=registered%40testuser.com valid": { email_known: true },
       "get /wsapi/have_email?email=registered%40testuser.com throttle": { email_known: true },
       "get /wsapi/have_email?email=registered%40testuser.com ajaxError": undefined,

resources/static/test/qunit/shared/network_unit_test.js

@@ -102,10 +102,19 @@
     network.logout(function onSuccess() {
       ok(true, "we can logout");
       start();
-    }, testHelpers.unexpectedFailure);
+    }, testHelpers.unexpectedXHRFailure);
   });
 
 
+  asyncTest("logout with 400 failure - user already logged out", function() {
+    xhr.useResult("not_authenticated");
+
+    network.logout(function onSuccess() {
+      ok(true, "we can logout");
+      start();
+    }, testHelpers.unexpectedXHRFailure);
+  });
+
   asyncTest("logout with XHR failure", function() {
     failureCheck(network.logout);
   });