app.user returns false instead of undefined if logged out, fix #2723

public/javascripts/app/app.js

@@ -6,7 +6,7 @@ var app = {
 
   user: function(user) {
     if(user) { return this._user = user }
-    return this._user
+    return this._user || false
   },
 
   initialize: function() {

spec/javascripts/app/app_spec.js

@@ -7,5 +7,11 @@ describe("app", function() {
 
       expect(app.user()).toEqual({name: "alice"});
     });
+    
+    it("returns false if the current_user isn't set", function() {
+      app._user = undefined;
+
+      expect(app.user()).toEqual(false);
+    });
   });
 });