Don't emit ERROR until a keepalive poke fails

This accomplishes the same as
https://github.com/matrix-org/matrix-js-sdk/pull/216/files, but
without the client waiting 110 seconds for a sync request to time
out. That is, don't display an error message a soon as a sync
request fails, since we should accept that sometimes long lived
HTTP connections will go away and that's fine.

Also:
 * Use request rather than deprecated requestWithPrefix
 * http-api: The empty string may be falsy, but it's a valid prefix

lib/http-api.js

@@ -351,7 +351,7 @@ module.exports.MatrixHttpApi.prototype = {
      */
     request: function(callback, method, path, queryParams, data, opts) {
         opts = opts || {};
-        var prefix = opts.prefix || this.opts.prefix;
+        var prefix = opts.prefix !== undefined ? opts.prefix : this.opts.prefix;
         var fullUri = this.opts.baseUrl + prefix + path;
 
         return this.requestOtherUrl(

lib/sync.js

@@ -406,7 +406,7 @@ SyncApi.prototype.sync = function() {
 
             self._sync({ filterId: filterId });
         }, function(err) {
-            self._startKeepAlives().done(function() {
+            self._startKeepAlives(0).done(function() {
                 getFilter();
             });
             self._updateSyncState("ERROR", { error: err });
@@ -546,12 +546,17 @@ SyncApi.prototype._sync = function(syncOptions) {
         console.error(err);
 
         debuglog("Starting keep-alive");
-        self._syncConnectionLost = true;
+        // Note that we do *not* mark the sync connection as
-        self._startKeepAlives().done(function() {
+        // lost yet: we only do this if a keepalive poke
+        // fails, since long lived HTTP connections will
+        // go away sometimes and we shouldn't treat this as
+        // erroneous.
+        // We sent the first keep alive immediately because
+        // of this.
+        self._startKeepAlives(0).done(function() {
             self._sync(syncOptions);
         });
         self._currentSyncRequest = null;
-        self._updateSyncState("ERROR", { error: err });
     });
 };
 
@@ -874,9 +879,15 @@ SyncApi.prototype._pokeKeepAlive = function() {
         }
     }
 
-    this.client._http.requestWithPrefix(
+    this.client._http.request(
-        undefined, "GET", "/_matrix/client/versions", undefined,
+        undefined, // callback
-        undefined, "", 15 * 1000
+        "GET", "/_matrix/client/versions",
+        undefined, // queryParams
+        undefined, // data
+        {
+            prefix: '',
+            localTimeoutMs: 15 * 1000,
+        }
     ).done(function() {
         success();
     }, function(err) {
@@ -888,6 +899,13 @@ SyncApi.prototype._pokeKeepAlive = function() {
             // responses fail, this will mean we don't hammer in a loop.
             self._keepAliveTimer = setTimeout(success, 2000);
         } else {
+            // If we haven't already marked this sync
+            // connection as gone-away, do so now and
+            // emit an error.
+            if (!self._syncConnectionLost) {
+                self._syncConnectionLost = true;
+                self._updateSyncState("ERROR", { error: err });
+            }
             self._keepAliveTimer = setTimeout(
                 self._pokeKeepAlive.bind(self),
                 5000 + Math.floor(Math.random() * 5000)