Disallow XHR streaming when running the test suite

There seems to be some sort of bug involving PhantomJS and XHR
streaming messages.  When successive pages are loaded that use XHR
streaming, PhantomJS seems to think the second one never finishes
loading and therefore hangs.

(imported from commit db93b4cab816f1fdc3f3f543c9394b1cba8abedb)

static/js/socket.js

@@ -14,6 +14,11 @@ function Socket(url) {
 
     this._supported_protocols = ['websocket', 'xdr-streaming', 'xhr-streaming',
                                  'xdr-polling', 'xhr-polling', 'jsonp-polling'];
+    if (page_params.test_suite) {
+        this._supported_protocols = _.reject(this._supported_protocols,
+                                             function (x) { return x === 'xhr-streaming'; });
+    }
+
     this._sockjs = new SockJS(url, null, {protocols_whitelist: this._supported_protocols});
     this._setup_sockjs_callbacks(this._sockjs);
 }

zerver/views/__init__.py

@@ -704,6 +704,7 @@ def home(request):
     # These end up in a global JavaScript Object named 'page_params'.
     page_params = simplejson.encoder.JSONEncoderForHTML().encode(dict(
         debug_mode            = settings.DEBUG,
+        test_suite            = settings.TEST_SUITE,
         poll_timeout          = settings.POLL_TIMEOUT,
         have_initial_messages = user_has_messages,
         stream_list           = register_ret['subscriptions'],